The struggle to determine US carrier design doctrine was intense. Only bitter war experience would resolve the decade-long debate.
Ultimately, the CV(Battle) was born.

THE BATTLE CARRIER (CVB)

The Midway Class of armoured flight deck aircraft carrier was no compromise. Its primary purpose was to range the largest practical single strike group. It was to carry as many aircraft as possible. It was to be capable of defending itself. And it was to be resilient in the face of battle damage.

The proposed CVBs were huge. With good cause.

Their internal volume enabled adaptability. Their endurance accommodated global operations. Their strength facilitated new generations of heavier jet-based aircraft.

The final design was for a 300.5m long, 41.5m wide carrier capable of 33 knots. With three elevators and two catapults, the 45,000 ton ship also had the space and facilities needed to provide the sustained operation of 133 aircraft. Its contentious secondary armament was resolved to be 18 of the new 5in/54cal guns. And the flight deck between the two in-line lifts would be protected by 3.5in armour plate.

This would protect the 379 officers and 3725 enlisted crew.

SECOND THOUGHTS

In July 1942, construction of the lead ship – to be named USS Midway – was approved by US Congress. In August, contracts were awarded for the construction of four CVB type carriers (Battle Carriers).

But President Roosevelt hesitated. He did not initially sign off on the contracts as he was worried about long construction times and concentration of resources.

He challenged his chief of navy, Admiral Earnst King, to justify their build over a swarm of smaller 11,000 ton light fleet carriers of a similar vein to that of the Royal Navy’s Colossus class.

Admiral Nimitz waded into the debate, expressing a lack of enthusiasm for either option: “(Midway was) unnecessarily large and unwieldy, and concentrating too great a percentage of strength in one hull … (But) the view is generally held that the 11,000 ton vessel is too small to meet the requirements of a first line carrier.”

His opinion, and that of other Pacific Theatre commanders, was speed of delivery was imperative. And that meant an evolution of the Essex design.

Admiral King, however, argued the navy needed to think beyond its immediate needs. So he found a compromise. Production of the 27,000 ton Essexes would not be slowed if the 45,000 ton CVBs were to take over the docks set aside for the now cancelled Montana-class battleships.

With the rapid supply of Essexes assured, President Roosevelt finally gave his seal of approval on December 29, 1942.

USS Midway was delivered in September 1945.

VINDICATION

While not received with great enthusiasm by all the 1945 US Navy senior staff, the three CVBs would eventually prove their true value postwar.

Size meant flexibility. And the light (though not exactly open) hangar also proved advantageous. Its structural adaptability enabled the Battle Carriers to easily adopt the new British angled flight deck and steam catapult innovations.

In October 1952, the CVB (Battle) was redesignated the CVA (Attack). The Project 110 rebuild produced the world’s first “supercarriers”.

All the features of the reworked CVBs produced the progenitor of the later Forrestal, Enterprise and Nimitz class ‘Super Carriers’.

 FLIGHT DECK

Stark, angular lines dominate every view of the floating museum USS Midway of today. But the ship was originally designed and built with an axial flight deck similar to that of the Essex and Yorktown classes before it.

Despite their great size, this gave the CVB’s the same challenges in operating aircraft as their predecessors. They needed enough clear space between the front edge of the flight deck and the aircraft range to suit variable wind-over-deck conditions. The aft lift could not be used during landing operations - nor could the centre-side lift. So aircraft had to be crowded together on the forward flight deck until landing was complete.

While the flight deck armour represented a major break from previous US carrier design, it was not integrated with the hull as a strength deck as in the Royal Navy designs. Instead, it was a superstructure. But this presented some challenges of its own.

The armour was heavy.

Such a significant percentage of weight so high in even a 45,000-ton ship resulted in a high metacentric height. This meant a substantial heel during high-speed turns, and a reduced ability to sustain a serious list.

It also necessitated extensive bracing to prevent it from “racking”, or deforming, due to warping and hogging as the ship punched through the waves. (The CVB class had a tendency to do this, instead of “riding” waves, due to their weight and hullform).

This entailed a lattice of heavy girders being erected above the 2inch steel hangar deck, which formed the ship’s main strength deck.

The armour did not extend over the flight deck’s entire 924ft length. The extra displacement needed to balance and support such extensive heavy superstructure would have been prohibitive.

The deck armour, like in British and Japanese practice, therefore only extended over the 692ft-long three-bay hangar. The 3.5in STS (Special Treated Steel) was placed between the two centreline lifts from frames 46 to 175.

The unarmoured steel deck between the forward lift and the bow was stressed to support the launch of a 13ton aircraft. The aft flight deck structure was rated for 11 tons, as it was assumed aircraft ordnance and fuel would be consumed before landing.

The British innovation of integrating an armoured flight with the strength deck would eventually prevail It was more weight efficient. And it was stronger.

This was why the CVB’s successors, the Forrestal-class supercarriers, adopted a deeper hull design with the strength deck at flight-deck level. This lifted its freeboard considerably over that of the Midways and allowed additional weight to be dedicated to flight group operations and protection.

HANGAR

The blast from a 2200lb bomb and multiple 1100lb bombs in HMS Illustrious’ armoured-box hangar in 1941 created pressure pulses that buckled the forward lift. They were also implicated (along with near-misses) in the sagging of the forward hangar deck. 

This was seen as vindication by USN designers of their prewar open hangar philosophy. It had argued open hangars would allow such blasts to vent with minimal effect. 

The fate of IJN Taiho supported this. Its unarmoured - but enclosed - hangar became a massive fuel-air bomb that cracked the 3.5in armoured flight deck and blew out large portions of the ship’s sides.

But war experience would also prove blast compression was not limited to enclosed hangars, as photos of Enterprise’s lift rocketing skyward on a plume of smoke attest. 

The conclusion: Hangars were vulnerable. Hangars were dangerous.

This is why the CVB hangar was divided into five individual compartments, each separated by 40-to-50 pound (1 inch to 1.25 inch, 2.5 cm to 3.2 cm) STS (Special Treatment Steel) transverse bulkheads. These extended all the way from the hangar deck to the flight deck.

Each was fitted with a large door to allow aircraft to move between them.

The hangar deck itself was armoured. This also formed the ship’s main strength deck. As such, two courses of 40-pound (1 inch or 2.5cm) STS were laid between frames 35 and 192.

While open sides allowed air to fan hangar fires - something HMS Illustrious and Formidable were able to prevent - BuShips believed the rigid armoured “box hangar” concept magnified the damage done to the aircraft it contained.

BuAer was adamant carriers needed hull openings to allow aircraft to warm up before being ranged on deck. Only this way, they argued, could multiple strikes be launched as rapidly as possible.

So the CVB design persisted with the open hangar concept.

Barely.

The CVB’s aircraft utility space ended up being much less open than that of an Essex.

There were no side bays through which aircraft could be loaded. As a result, the ship's flight-deck crane had to be used to haul them up to the three lifts.

Essentially, only the opening produced by the deck-edge lift remained. 

In practice, the CVB open hangar ended up being little more than an unarmoured “box” hangar.  Like that of Taiho’s.

Its sides were enclosed by 5in gun sponsons, structural frames, braces, access ladders, hatches, winches, ammunition lifts, avgas stations, bollards, rope lockers and boat bays.

BuShips recongised the situation. Even if it didn’t admit it.

The opening provided by the single deck-edge lift could not be expected to vent all exhaust fumes from 130 aircraft warming up their engines. This necessitated the adition of powerful electric fan ventilation ductwork. 

Without it, aircrew and maintenance personnel would be poisoned.

LIFTS & FLIGHT DECK Equipment

A pair of hydraulic powered catapults were fitted to the bow. And side-launch catapults were included in initial design work until they proved impractical in service aboard the Essexes.

The H4-1 catapults were an extended version of those used aboard earlier ships. They proved capable of accelerating a 28,000 lb aircraft to 90mph.

Arresting gear as fitted consisted of fourteen Mk 5 Mod 0 winch engines,  attached one to each side of the seven arresting cables crossing the flight deck. Five were positioned aft of the aft axial lift, one over it, and one on the bow immediately before the catapults.

There were also six retractable crash barriers across the flight deck’s centre, alongside the island.

As completed, the Midway CVBs had two centreline elevators and one deck edge elevator.

The axial arrangement was traditional. Their position at either end of the hangar allowed optimal strike-down and range-up access for aircraft.

USS Wasp was commissioned in 1940 with the first example of a deck-edge elevator. This quickly proved its value when it came to moving aircraft with minimal interruption to ongoing flight operations.

The CVBs, like the Essexes, stuck with the innovation.

This smaller lift extended outboard of the flight deck immediately opposite the island. Without it, an “on paper” deck park of as many as 130 aircraft would be impossible to assemble promptly.

But it wasn’t entirely successful.

USS Midway suffered from the same low freeboard often levelled as a criticism of the earlier Illustrious class. But, in her case, this meant the deck-edge elevator was prone to shipping water in any kind of sea state.

FIRE SUPPRESSION

The CVB design had a network of aviation fuel lines connecting the hangar to fuel bunkers buried deep within the ship. It was hoped their remote position, coupled with the deck and belt armour, would reduce their exposure to battle damage.

The fuel lines, however, were necessarily more exposed.

So fire-prevention measures included vacuum pumps and seawater replacement removing residual fuel (and its vapours) from the lines.

But the risk that the hangar would become a giant fuel-air bomb persisted.

Aircraft were to be refuelled while stowed below. This could be spilled by accident or direct enemy action.

Dispersing any gasoline fumes released was therefore a priority.  It simply could not be allowed to build up.

There were no shuttered access bays like in the Essex class. And only the one significant opening was that produced by the side lift (when functional).

The problem, as with exhaust fumes, was considered solved by adding extensive fan ventilation ducting.  And this network could be shut down to deprive the hangar of oxygen in the event of fire.

Like the Illustrious class, fireproof curtains could be rolled out to localise fires to any combination of the five individual hangar sub-compartments.

Firefighting posts were positioned at regular spaces along the walls. These were divided into four sections and accessed via three armoured fire doors.

Each section controlled its own firefighting system. Extra attention was paid to the coverage and resilience of these piped sprinkler and fog-foam networks to maximise survivability.

It was hoped this combination of active and passive measures would prevent schrapnel and fires from spreading as extensively as they did in the cases of USS Franklin and Bunker Hill.

ISLAND

The Bureau of Ships wanted the CVBs to have as small an island as possible. This command space impinged upon useable flight deck area. It also contributed to cross-deck airflow turbulence.

But the Midways had 12 boilers. And adequate ventilation meant a prominent stack was inevitable.

One design decision, however, sticks out.

The CVB was allocated an armoured forward conning tower and pilot house. Previously, it had been a feature limited to battleships, battlecruisers and heavy cruisers.

Its presence on an aircraft carrier was to prove immediately unpopular.

The armoured trunk could only be accessed via a few unwieldy blast doors. And the interior space it protected was limited.

None of this helped facilitate air operations. And the 6.5inch armoured enclosure added considerable topweight.

It was also unbalancing, positioned as it was on the starboard deck edge. So much so that the starboard belt armour had to be cut down in thickness and coverage to compensate.

Such was the outcry that USS Midway returned to dock after less than six months active service. The armoured conning tower was ripped out, and a more open and spacious command facility installed, including multiple catwalks from which deck activity could be observed.

This rebuild considerably lightened the Midway’s starboard side. And restoring the belt armour to 7.6 inches was impractical, so permanent ballast was the only option.

Both the USS Coral Sea and Franklin D. Roosevelt were completed with a new-design bridge. But they also retained the thinner starboard belt. These heavy armour plates had already been cast and fitted.

Protection

In 1940, bomb manufacturers insisted they could produce a new 1750lb design capable of piercing 7in of deck armour.

This came as a shock to naval architects.

There was no way such a thickness could be supported on the upper deck of a battleship - or aircraft carrier. Stability and structural strength ruled it out as a possibility.

The answer, as with the Montana-class battleships, was to split the weight of armour over several decks.

The CVBs were built with three layers of horizontal protection.

The Flight Deck between the two centreline lifts was 3.5in (88mm) armour plate.

The Hangar Deck was 2in (51mm) thick STS.

The lower Third Deck was also 2in (51mm) STS.

Side protection was also relatively heavy.

Since the 1920s, US Navy design studies had concluded the greatest threat to a fast carrier was a surface engagement with 8in cruisers. 

This fear held firm in the early 1940s.

After all, hadn’t HMS Glorious been sunk by German battlecruisers? And HMS Formidable had engaged Italian cruisers (admittedly with only one salvo) in the night action at Matapan.

So the threat of encountering marauding Japanese 8in cruisers was regarded as very real.

Protecting an aircraft carrier in these circumstances was a big ask.

The solution was to give the CVBs a 7.6in (193mm) armoured belt.

But the requirements also called for the new class to be completed with an armoured conning tower as the core of its small island bridge. That much weight, off-centre and so high in the ship, had to be compensated for.

As a result, the thickness of the starboard armoured belt was reduced to 7in (178mm). It was also “trimmed” by tapering it to 3in at the edges.

In contrast, the 7.6 in port-side armour belt was extended by three feet. The extra weight would act as a counterbalance.

But British battle damage reports supplied under intelligence sharing arrangements from 1939 to 1942 revealed armour was not enough.

Ships needed to be strong. 

They needed to be well subdivided. 

They needed ample pumps, fire hoses and damage control stores.

The 45,000 ton CVBs were allocated thicker than usual hull plating. And 26 transverse bulkheads, each 6.2in (160mm) thick, were added to reduce the spread of shrapnel, fire and flooding..

“The Midway class had a well subdivided arrangement of the machinery spaces underwater, a simple copy-paste of the Montana-class battleship system, more evolved than the Iowa class, “ states Naval Encyclopedia

“Instead of eight main engineering compartments, the Midway-class had 26 in total, with no less than twelve boiler rooms off the centerline, four widely separated engine rooms. This ensure the least risk of a critical flooding, even if hit by several torpedoes.” 

Such survivability, however, came at a price.

USS Midway and her sisters had a poor reputation among their crews. They were cramped and uncomfortable. And movement often involved going far out of one’s way to find access.

ARMAMENT

The CVB’s gun armament was a contentious issue. 

Were dual-purpose mounts an effective compromise? Was the perceived threat of Japanese cruisers sufficient to make dedicated 8in weapons necessary? Or was the air threat more persistent and therefore important?

Lexington and Saratoga had been completed with 8in guns fore and aft their island. They gave the carriers a chance to shoot back if intercepted by Japanese heavy cruisers.

But it was the early war experience of HMS Illustrious and HMS Formidable in the Mediterranean settled the matter for BuShips.

In 1942, CVB designers selected the new DP gun - the 5”/54 Mk 39 - originally intended for the cancelled USS Montana-class super-battleships. 

The CVBs were fortuitously big.

That meant more space along the hull for gun sponsons, and greater capacity to carry their weight. This resulted in the heaviest gun armament on a US carrier since the 1920s battlecruiser rebuilds.

Each 40-ton 5-inch single-gun mount had a crew of 17.

There were 18 such mounts set on barbettes recessed into the hull outboard of the Hangar Deck. This isolated them from flight deck and hangar operations.

The Essex-style twin-5-inch/38 gun deck mounts were done away with. Eight of that class’ 12 guns were fitted in twin turrets, two forward and two aft the island. Not only did these mounts take up valuable flight deck space, their operation also presented a blast hazard to crew and aircraft.

The 5”/54 was a significant improvement over the 5”/38. They could reach out to 23,000m as opposed to 16,000m. And they fired a heavier 70lb shell (against 55lb). 

By 1943, air defence had cemented itself as the absolute priority.  Any Japanese cruiser attack would have to be seen off by the carrier battle groups' escorts, and aircraft.

By 1945, every scrap of spare space had to be dedicated to anti-aircraft guns to counter the new kamikaze threat.

As delivered, the USS Midway carried 21 quad 40mm/60 Mk2 mounts (for a total of 84 barrels). This was almost triple the number on an Essex. 

Each mount had a crew of 11 and individual radar fire control.

Exactly how many 20mm guns were originally to be installed is a matter of debate. Most sources put it at 28 barrels. Others at 68. Either way, 10 twin 20mm mounts were actually fitted to USS Midway upon her launch in September 1945. 

All 20mm and 40mm mounts were removed by the end of the 1950s as they were regarded as ineffective against fast jets.

CVB43 (USS Coral Sea) was completed without four of the single 5”/54 mounts. This measure was to improve seakeeping by reducing weight. Only 19 quad 40mm were fitted. She had no 20mm mounts.

Machinery

A bigger carrier needed more horsepower if it was to meet fleet speed requirements.

So the Midway class was given the same 212,000 shaft horsepower steam-turbine plant used by the Iowa (BB-61)-class battleships. The Essex class had 150,000shp.

Four Westinghouse Steam turbines were divided between cruise, inner low-pressure, and top speed, outer, high-pressure units.

These  turbines were driven by steam from twelve Babcock & Wilcox boilers operating at 565 psi and 850°F (450°C). 

This powerplant was connected to four shafts, each fitted with an 18ft (5.4m) propeller, weighing 22 tons.

Improvements over the system used in the Iowa class produced unexpectedly good results, enabling the Midway class to easily reach their designed fleet speed of 33 knots. 

But things would rapidly change.

USS Coral Sea and FDR came off the slipways a little slower due to extra weight. It fell to 30.6 knots after the 1950s rebuilds. But it was later restored to 31.6 knots.

A war load of 10,032 tons of fuel (as opposed to the freeboard-restrained 6004 tons for peacetime) meant the CVB could cross 15,000 nautical miles (27,800km) at 15 knots.

An Essex was capable of about 15,440 nautical miles (28,600km).

SEAKEEPING

Armoured flight deck critics were adamant: speed and maneuverability were a much better defence against bombs and torpedoes.

But war damage report after war damage report put paid to this argument.

What was needed was balance.

But what form this would take was a constant battle.

Demands for extra armour, extra aircraft and extra fuel meant extra beam had to be added to balance extra topweight. Extra beam meant more drag, so the hull needed to be lengthened to create a more efficient hydrodynamic shape.

As with the British Illustrious and Japanese Taiho, the armoured flight deck had to be kept as low as possible.

This meant the CVBs were given 17.5 tall hangars. And the flight deck sat four feet closer to the water than an Essex.

It also meant their waterline beam was 121 feet (37m), precluding use of the Panama Canal.

USS Midway immediately experienced problems upon commissioning.

Her low freeboard and long length resulted in water being regularly shipped over the open bow and gun sponsons into the hangar deck. 

The carrier pitched and rolled in heavy seas because of its slim and low form. Its length caused it to plunge in even moderate seas.

“Also in easy weather, they "corkscrewed" so much it precluded any landing operations,” states Naval Encyclopedia.

Spray would douse aircraft on the deck part and catapults. And use of the side elevator was restricted.

“The high metacentric height also produced excessive heel in hard rudder turns,” Naval Encyclopedia adds.

Solutions were urgently sought.

The type’s freeboard simply had to be raised.

Remedial measures were taken aboard USS Coral Sea and USS Franklin D. Roosevelt. This entailed fitting fewer 5-inch/54 guns, 40mm and 20mm mounts. Along with limits on stores and fuel.

The bow was later fully enclosed on all three ships along the lines of the British “Hurricane” design. But the class would remain “wet” for their entire careers.

At flank speed (30 knots), the USS Midway (CV-41) possessed a tactical diameter of roughly 990 yards (approximately 905 meters). The ship would lose about 60 per cent of her speed in the process.

AIR GROUP

The CVB was 20 per cent wider and 10 per cent longer than the previous Essex class. That resulted in a 50 per cent increase in aircraft carrying capacity. In September 1945, USS Midway was assigned a specification air group consisting of:

• 64x F4U-4 Corsairs

• 64x SB2C-5 Helldivers 

• 4x F6F5P (photo reconnaissance) Hellcats

On paper, all 132 aircraft could be ranged on the flight deck. In practice, this proved beyond the practical limits of the deck crew and flight equipment. Which may be why USS Midway did not go to sea with her maximum air group in 1945.

Instead, she carried 120:

• 57x F4U-4 Corsairs

• 59x SB2C-4E Helldivers

• 4x F6F5P Hellcats

Ultimately, the CVB’s effective striking power would be little stronger than that of an Essex.

At the centre of the problem was the World War II USN concept of “complete carrier evolution”. This is the time it takes to launch and land a strike group. 

With estimated 20 second launch and 40-30 second landing intervals, this would inevitably add up to a significant amount of time for 130-140 aircraft. Then you have to take into account the inevitable mistakes and accidents.

Even with a CVB’s enlarged axial flight deck, the catapult and over-bow launch rate and arrested recovery rate offered no great improvement over the Essex design.

Accounts from USS Midway’s 1945 operations suggest only about half its air group could be cycled as a strike at any one time.

Making matters even more difficult was the axial-alignment of the World War II era flight deck. Take-off and landing-on operations could not be conducted simultaneously. 

The consequence of so many aircraft operating from one deck meant the CVB would have to spend at least six hours of a day sailing into the wind in order to launch and recover its specified six deck-load strikes. And this almost always led the carrier away from the desired direction of travel.

This would only be overcome with the advent of the angled flight deck. Simultaneous launch and landing would reduce the time needed for the operational six-strike requirement to four hours.

By this time the size of the Midway came into its own. Aircraft sizes were growing dramatically. And the CVBs could easily be modified to accommodate them.