16 August 1940. Newcastle-upon-Tyne. England.
Sir John Carden and Leslie Little were looking at a newly arrived 75mm M1897 gun and they both felt like slapping their own foreheads. There was no way on God’s green earth that they’d be able to shoehorn that thing into a turret to act as a close support gun. Then the air raid siren began it wail and the two men, with their retinue, followed the workers off the shelters. As they were going, they passed a number of partially completed vehicles and other things they’d experimented with. The idea of the Birch Gun, a self-propelled artillery piece was something Carden had long planned. It had got to the point where one of the A10 hulls, adapted to take the Meadows DAV engine, had been set aside as the trial vehicle.
Seeing the hull sitting there reminded Carden that progress on it had stalled because the Royal Artillery had needed every gun it could get its hands on for France. As they two designers sat in the shelter, they agreed that rather than sending the 75mm gun back to whence it had come, since it wasn’t too different in size and weight to the 25-pdr, why not get it finished and show it off to the Royal Artillery at Farnborough? If it worked, and neither Carden nor Little could see that it wouldn’t, then once more 25-pdrs became available, then the Royal Artillery might want some Birch Guns for the Royal Horse Artillery.
When the sirens wailed again for the all-clear the two men got the drawings out of the safe to review them. The changes to fixing the 75mm into the hull took only a little effort to change from the 25-pdr. Over a cup of tea, they talked to the team who’d worked on the hull layout, and told them what they were proposing and how they’d like it done. There was a certain amount of head scratching and humming and hawing, not unusual with these men, and then, agreement. Everything was literally in one place, the hull, the engine and now the gun. Some more thinking out loud, and then the estimate that it would ready mid-September, Luftwaffe allowing.
While they were there, the plans for the anti-aircraft mount were brought out of the safe too. This was based on using an A9 hull, again adapted for the Meadows engine, something that was also sitting at the side of the factory. Once again, it had been the difficulty in getting guns had caused the hold up. All sorts of combinations of guns had been suggested, machine guns and cannons, and then the story of how one the A11s had shot down a Stuka at Arras was retold. That was when one of the Charge Hands mentioned that there were still two of the pompoms that had been used in the A11s laying around somewhere. After some serious questioning it turned out that there had been some fault found on them, so they’d been replaced by two other guns. As with much of life, no one had bothered to do anything about the broken ones, so they were still sitting in boxes somewhere up against a wall. Getting hold of a twin mount from the naval gun section of the factory complex wouldn’t be a problem, at least not officially. There was a backlog in making the guns, but nothing holding back the mounts. If no one asked too many questions, they could at least marry the twin mount to the hull of the tank. They could then check if that worked with the weight and balance of the two guns.
Someone else on the team had a brother-in-law on the pompom line, so maybe, for a small investment in a bottle of something, the fault in the guns could be looked at, hypothetically, to see if they could be fixed. All going well, and some of those in management didn’t look too closely, a prototype Vanguard SPAAG could possibly be ready in about the same time frame, maybe a week or two later. Like using the 75mm M1897 on the Birch Gun, the twin pompom wouldn’t necessarily be what the army ended up with, but it would prove the concept effectively enough. Perhaps, Leslie Little mused, once enough of the new Oerlikons became available, they’d be a better choice for the Vanguard. Carden wasn't sure he agreed, he thought the army would be keener on using a single Bofors 40mm.
?) and just build it with a shield and bigger traverse. The Priest M7 / Sextons can come along when their little brother is deemed ineffective.