Could they not fit it with 37mm cannon also ?
not a good idea to HO that one, even in a 410....
Initially, all A-26Bs were supposed to be produced with a 75mm cannon but only the early blocks (15 A-26B-5s) came out of the factory with a 75mm cannon and 2x .50 caliber machine guns. A new all purpose nose was introduced with the A-26B-10-DL block that included different gun packages the USAAF tested out that are listed below.
75mm cannon with 2x .50 caliber machine guns
75mm cannon with 1x 37mm cannon
2x 37mm cannons
37mm cannon with 2x .50 caliber machine guns
37mm cannon with 4x .50 caliber machine guns
6x .50 caliber machine guns
The USAAF decided to go with the 6x .50 caliber nose package for a few reasons. The primary reason was that cannon equipped attack planes didn't offer any advantages over 'strafer' versions, as the USAAF found that strafer models were just as effective in destroying hardened targets with machine guns and rockets as the cannon equipped attack planes like the B-25G/H. Another reason was the slow rate of fire of the 75mm and 37mm cannons and the unreliability of the 37mm cannon. Another reason was logistics, it was far easier to use a universal weapon package for the Invader than having different types of guns and ammo. As far as I know, none of the early A-26B-5s that were produced with the 75mm cannon ever saw any operational service and I believe had 75mm cannon removed and replaced with the standard 6x .50 caliber machine guns.
ack-ack
