Wi: Bigger and larger IMPLACABLE class Carriers

[Zen9]

POD 1935

Instead of the ten 23,000 ton aircraft carriers carrying 36 aircraft each, the Admiralty decided that it required ten 27,000 ton ships carrying 72 aircraft each.

27,000 tons was the maximum possible displacement for an aircraft carrier under the Washington and Fist London Naval Treaties. ITTL it was carried over into the Second London Naval Treaty instead of being reduced to 23,000 tons.

The resulting ship was an enlarged Implacable, rather than an enlarged Illustrious because its machinery produced 148,000shp driving 4 shafts rather than 111,000ship driving 3 shafts.

The enlargement was to allow the ship to have two full length hangars, which were 62 feet wide and at least 16 feet high. These are the hangar dimensions on the OTL ships.

View attachment 474375​

Except that I have seen some drawings of the Audacious design, which show that the length of the hangars was 364ft between the lifts and that the upper hangar and an extension of 48 feet in front of the forward lift, which made the total length up to 412 feet.

The ship was to be welded, be fitted with high-pressure boilers and an AC electrical system instead of the normal DC to save weight.

In common with OTL the 10 ships were to be ordered at the rate of 2 per year, starting at the 1936-37 Navy Estimates. Eight of the ten ships were ordered before September 1939 as follows:

1936-37 - Illustrious and Victorious
1937-38 - Formidable and Indomitable
1938-39 - Invincible and Inflexible
1939-40 - Implacable and Indefatigable​

The two ships planned for the 1940-41 building programme were eventually built as the OTL Audacious class aircraft carrier Ark Royal and a fourth Audacious class which was built in place of the OTL battleship Vanguard.

To be continued...

Moving from three sets of plant and shafts to four imposes some restrictions on rates of production.
This is a full 33% increase in production per ship. Not trivial.
This might impose a delay in construction.
Flipside is higher regular production of large warship plant machinary, props and shafts delivers some efficiency per unit due to higher continuous production.
Thus might also drive thoughts towards the future and the need for research and testing facilities to cope with SHP figures above 50,000shp. The limit of UK facilities at the time.

 

[NOMISYRRUC]

Moving from three sets of plant and shafts to four imposes some restrictions on rates of production.
This is a full 33% increase in production per ship. Not trivial.
This might impose a delay in construction.
Flipside is higher regular production of large warship plant machinary, props and shafts delivers some efficiency per unit due to higher continuous production.
Thus might also drive thoughts towards the future and the need for research and testing facilities to cope with SHP figures above 50,000shp. The limit of UK facilities at the time.

While it has been said that one can do anything with statistics the following is relevant.

IOTL a grand total of 5 battleships, 4 aircraft carriers and 14 cruisers were ordered in the 1936-37 and 1937-38 building programmes.

I thought the KGVs had the same 3-shaft plant as Illustrious, Formidable, Victorious and Indomitable so it was really an increase from 27 sets of plants and shafts to 31 or an increase of about 15%. However, when I got my copy of Conway's 1922-46 to check the KGVs had 4-shaft plants, which would increase the total from 32 to 36, which is an increase of about 13%.

The substantial increase is the 1938-39 and 1939-40 building programmes. IOTL 4 Lion class and 2 Implacable class were ordered. Both classes had 4 shafts, which makes a grand total of 24. However, ITTL 4 aircraft carriers are ordered under these building programmes instead of 2. That increases the total from 24 to 32 or by 33%.