3"20ctw AA

[BMG50]

I have been reading a good book called AA Command by Colin Dobinson which talks about WW 1&2 air defences. It seems that the 3" 20ctw was a popular AA gun during WW1, what type of projectile fuze and case are we looking at and how was it marked up. I have seen some dodgy looking cases, some cut down but have no reference to this round for AA use.

 

[Tony Williams]

The cartridge case is 420 mm long with a 116 mm rim diameter. During WW2, the same case was used for the 77 mm tank gun fitted to the Comet tank, with different loadings.

In WW1 the standard projectile was a 12.5 lb shrapnel, fitted with a Time & Percussion fuze No. 84. There was also an HE shell filled with amatol, with T&P fuze No. 85, and a 12.2 lb incendiary, fitted with a No. 185 Time fuze.

 

[BMG50]

I assume if the casings were used for the 77 then there are not many about. Are they a difficult round to find?

 

[2pounder]

3in 20cwt cases dated WWI are quite common, but it was virtually obsolete by WWII (but guns available ) as planes too fast and too high so later dated cases are rarer. Cases marked for 77mm rare, but also have one marked for anti submarine use but modified by reducing the length to below the shoulder.

 

[Vasco Da Gama]

I thought to post a couple of pictures of a restored 3in 20cwt round I have had for many years. The case was picked up in Malta in the early 1980's, before airport security was so intense! I think the paint markings on the case base indicate a HE shell with smoke box. The round is also pictured against the competition, a 3.7in and a 88mm Flak. As mentioned the 3in 20cwt was outclassed by the start of WW2 but I guess many served in parts of the Empire until sufficient 3.7in came along.

 

[Tony Williams]

Even in WW2 the 3 inch 20 cwt did have some advantages: it was a much smaller, lighter and handier device than the massive 3.7 inch, so much easier to ensure it was in the right place when needed.

 

[kahu1]

There is a book about an AA battery, using initially the 3" 20 cwt, in Darwin during WW2. The title and in the content, was something like 'Use the WW1 Ammunition first'.

 

[BMG50]

A friend has a 3inch 20cwt but as pointed shot, quite a heavy lump dated 1945 i assumed they used this round for other things, anti tank or practice.

 

[tankbarrell]

The gun was mounted in a small number of Churchill hulls as a 3" gun carrier. These used a solid AP shot.

 

[ron3350]

I also have an AP-T projectile for the 3"20CWT. I wondered why they bothered to develop a different 3" AP-T projectile .
Also a case for submarine Star shell with a milled rim for ID Navy use.
British Mk11 cases. British, Australian & Indian cases MkV plus an Australian Drill wooden round.

 

[Darkman]

There is a book about an AA battery, using initially the 3" 20 cwt, in Darwin during WW2. The title and in the content, was something like 'Use the WW1 Ammunition first'.

I have a reprint of this book. Now called "Darwin Bombed" but originally titled "Use the 1916 Ammo First". It's a recount of a gunner's time with the 14th Heavy AA unit in Darwin, NT, Australia during WW2. The unit was originally equipped with 3" guns then in late 1941 they re-equipped with new 3.7" guns. But the 3" AA guns continued to be used in Darwin throughout WW2 up until about 1943-44. Attached is a gun drill photo from the book.

 

[Vasco Da Gama]

I thought to post a couple of pictures of a rebanded and repainted practise projectile for the 3in 20cwt. The P is covered by the yellow band but clearly present. The weight of the projectile is given as 16lbs, length from the top of the driving band is 222mm, the HE variant is 204mm. The practise projectile is in a 1918 case, also pictured is a 1945 77mm Comet case, alongside the 1918 case.

 

[ron3350]

I decided to show my 3" 20 Cwt items here.

AP 12 1/2 LB. 111T BS. FGC. 7/42. P. Repainted black.
1918 Navy Star shell with N in H/S and milled rim for ID.
1940 Navy Star shell with N in H/S and milled rim for ID.
Used on submarines I am told.

 

[BMG50]

I see that the WW1 AA projectile is quite different to the WW2 AA version being similar to a 3.7 in looks, are these AA projectiles very hard to find.

 

[Gspragge]

Tony is right and of course with smaller size every one can have one ~:tinysmile_fatgrin_t