Adolf Hitler wasn't interested in wonder weapons, because he thought Germany would win the war with conventional weapons before they were ready. Only when Germany had to go on the defensive, with Soviet counterattack and the United States' entry in the war on Britain's side, did Hitler start giving the wonder weapon projects like the A-bomb (1942) and the V2 (1944) the funding long denied them. It was such that a conventional "dirty bomb," far weaker then those dropped on Japan, was slated for 1946. Britain's defeat, and the United States' continued neutrality, negate the very factors that got the German A-bomb program its funding.
The SS are aware that Detective Archer does not share their beliefs, and that his wife was killed by German bombing. Yet they choose to keep him as the chief local policeman on a case they view as enormously important, rather than recruiting a more reliable collaborator. Great Britain, like all countries in Western Europe, had some pro-Nazi bodies to choose from.
A wanted woman risks arrest to personally warn Detective Archer. She could have sent a friend or a hired messenger.