Destroyers
At the POD the RNs had 192 destroyers completed and 30 under construction or on order. That is 180 RN, 5 RAN & 7 RCN completed and 24 RN & 6 RAN building or on order.
Under the First London Naval Treaty a destroyer laid down before 01.01.21 became over-age 12 years after its date of completion and a destroyer laid down after 31.12.20 became overage 16 years after its date of completion. Therefore:
- 113 were under-age because they were laid down after 31.12.20 and completed 1927-39. They would become over-age 1943-55 at an average of 8 boats (or one flotilla) a year.
- 79 were over-age because they were laid down before 01.01.21 and completed 1917-25 and became overage 1929-37.
Except that under the Second London Naval Treaty destroyers came under the category Light Surface Vessels (c) because they displaced less than 3,000 tons and were armed with guns not exceeding 6.1 inches in calibre. Ships of this category became overage 16 years after their date of completion regardless of when they were laid down. Therefore, under the extant Treaty the 79 oldest destroyers became overage 1933-41 instead of 1929-37. This included 5 that were under-age on 03.09.39 of which 4 would become over-age in 1940 and one that would become over-age on 15.04.41.
However, I'm sticking to the 1930 Treaty, because that's what Anthony Preston did in this book "Destroyers". The 79 old destroyers consisted of 9 flotilla leaders, 12 R&S class and 58 V&W class. The 113 new destroyers consisted of 81 of the A-to-I type (including 2 prototypes and 2 built for the RCN), 16 Javelin class and 16 Tribal class. The 30 destroyers under construction or on order were 8 Javelin class & 16 Lightning class for the RN and 6 Tribal class to be built in Australia for the RN. My information is different from
@EwenS. That is my sources says Australia ordered 2 Tribals in January 1939 and 4 more in May 1939 for a total of 6.
There were enough destroyers to form the required 22 flotillas each consisting of 8 or 9 ships. However, the ratio of over-age to under-age flotillas was 13:9 instead of 16:6. Fortunately, when the 24 destroyers building or on order for the RN were completed there'd be enough ships to form 25 flotillas with a 16:9 ratio of under-age to over-age destroyers.
IOTL
- The 8 L class were laid down October 1938 to March 1939. All before the POD.
- The 8 M class were laid down October 1939 to September 1940. All after the POD. Furthermore, one had to be laid down a second time on 18.08.41 due to damage sustained in an air raid, which won't happen ITTL.
- The 8 N class were laid down July 1939 to July 1940. That is 5 before the POD. One on 09.09.39 six days after the POD and 2 in 1940.
Therefore.
- 13 out of 24 were laid down before the POD. So no change there ITTL;
- One was laid down shortly after the POD. So unless @EwenS knows something to the contrary, no change there.
- 10 laid down after the POD. Of which 4 were laid down in the last quarter of 1939 and the rest were laid down in 1940. I have no idea how no European War affects that, but @EwenS might.
IOTL 13 out of 24 were completed before 07.12.41. That is 6 L class, 2 M class and 5 N class. My guess is that due to the factors explained by others all 24 would have been completed before the start of the Pacific War IOTL.
Except, at the POD, one old flotilla leader and 10 V&W had been converted or were being converted to AA & AS escorts. This involved removing the existing armament (including the torpedo tubes) and fitting two twin 4in AA gun mountings, 2pdr pompoms, 0.5in machine guns and a HACS. This was against a requirement for 4 flotillas. IOTL another 5 V&W class were taken in hand for the conversion when the European War started for a total of 16 including the Leader, which was enough for 2 flotillas, although one didn't have a leader. ITTL where there is no European War its very likely that a total of 4 old leaders and 32 V&W class would have been converted to form the 4 flotillas required.
These 4 flotillas weren't counted in the 22 flotillas. Therefore, the requirement was actually 26 flotillas of which 6 could be over-age with their original armaments and 4 over-age flotillas converted to AA & AS escorts. Therefore, the RN would be one flotilla short of requirements when the L to N classes were completed instead of having 3 that were surplus to requirements.
The K and L classes were built under the 1938-39 Estimates and the M & N classes were built under the 1939-40 Estimates, which in
@EwenS-speak are the 1938 and 1939 (Building) Programmes respectively. My guess is that the plan was to build one flotilla a year in perpetuity from the 1940-41 Navy Estimates onwards as that was the rate required to maintain a force of 16 flotillas that were less than 16 years old. I've no idea what designs of destroyers would have been built under the 1940-41 & 1941-42 Estimates for completion in 1942 & 1943 respectively or what at 07.12.41 was planned to be built under the 1942-43 Estimates for completion in 1944. However, if it was up to me I'd build more Lightnings or Tribals and as they were completed pass the A-to-I class down to replace the older destroyers in the lower-threat areas.
However, ITTL the number of destroyer flotillas may increase in the 27 months between September 1939 and December 1942 as the threat from the Kriegsmarine and Imperial Japanese Navy evolves. I'm not including the Regia Marina because countering that is what the Marine Nationale was for.
IOTL 10 destroyers of the A-to-I type were building in the UK for export at the POD and 8 of them were taken over by the RN. All 10 would have been completed and delivered by the outbreak of the Pacific War ITTL. IOTL the Argentine Navy had plans to order another 5 destroyers of this type and they might be under construction in UK yards in December 1941. But apart from that I haven't a clue about what other export orders might be in progress at that date.
What
@EwenS wrote about the destroyers that might be ordered for the RCN between the POD and December 1942 ITTL. My information (which may not be the same as his) is that the 4 Vickers-built ships were ordered on 05.04.40 & completed in 1943; the first 2 Canadian-built ships were ordered in July 1941 & completed 1945-46 and the last 2 Canadian-built ships were ordered in April 1942 & completed 1947-48. That is 6 before the start of the Pacific War and 2 afterwards. My guess is if that was the TTL sequence of events all 8 ships would have taken less time to build for reasons already explained better than I can by others (mainly
@EwenS).
Which brings us back to the 6 Australian Tribals. My guess is that all 6 would have been laid down before the start of the Pacific War and be built in a shorter length of time than the 3 that were eventually built ITTL. Arunta would have been completed before the Pacific War started and Warramunga might have been too. If the TTL Pacific War went on for as long as the OTL version it's likely that at least one follow-up order for more Tribals or a new fleet destroyer design would have been let.
I'm not doing the Hunt class in this points, because they were classed as (fast) escort vessels and if I write a message about how the construction of minor war vessels would have been altered between September 1939 and December 1942 they'll be included in that.
Summary added 08.05.25
I think the Royal Navies would have 216 destroyers on 07.12.41 ITTL, plus one or two of the Australian-built Tribal class. These were enough to form 25 flotillas (against an OTL requirement for 26) of which 16 were under-age (as per the requirement) and 9 were under-age (one short of the requirement).
137 destroyers completed 1927-41 formed the 16 under-age flotillas. They were 81 A-to-I type, 24 Javelin class, 16 Lightning class and 16 Tribal class. 79 destroyers completed 1917-25 formed the 9 under-age flotillas. They were 9 leaders, 12 R&S class and 58 V&W class. Four old leaders and 32 V&W class had been converted to AA & AS escorts.
At least 16 destroyers (2 flotillas) would have been under construction for the RN. One was in the 1940-41 Estimates (1940 Programme) and the other was in the 1941-42 Estimates (1941 Programme). They were laid down 1940-41 and were due to complete 1942-43. Another flotilla was planned for the 1942-43 Estimates (1942 Programme) to be laid down in 1942 and completed in 1944. I've no idea what type of destroyer they'd be.
If things had gone the same as OTL 4 Tribal class destroyers were under construction in the UK for the RN and 2 more would be under construction in Canada for the RN. Construction of all 6 destroyers was more advanced ITTL than it was IOTL.
In common with OTL 6 Tribal class were ordered from Australian yards in 1939. However, unlike OTL one or two had been completed and the other 4 or 5 were under construction.
