When Germany acquired a land border with Spain after the French capitulation in 1940, they took advantage of the opportunity to purchase Spanish firearms, and have them delivered across the French border to the town of Hendaye. A German inspection office was set up there for use with both Spanish arms and Unique pistols. The first purchases from Spain were Astra 300 and Astra 400 pistols – the 300s were fine, but in .380 and .32 caliber. The 400 was a more suitable service sidearm, but it was chambered for the 9x23mm cartridge which Germany did not use. So in 1943, a couple of German engineers visited Astra to see about production of a pistol more suited to the Wehrmacht use.
The result was the Astra 600/43, basically a model 400 rechambered for 9x19mm. It used a Navy pattern of magazine release instead of the 400’s heel release, and was generally much more what the German military wanted. Germany ordered 41,500 of them, and production began. The first delivery was in May of 1944, and a total of 10,500 were delivered to Hendaye before Allied advances into France made further deliveries impossible. These 10,500 guns were inspected at Hendaye, given WaAD20 proof marks, and distributed into the German military system. Astra continued to produce the guns through 1945 despite the inability to deliver (Germany had paid for them in advance, after all), and by the end of the war they had nearly 50,000 available.
Some were sold on the Spanish civilian market, and a few small sales were made to militaries worldwide (Portugal, Chile, Jordan, Turkey, etc) as well as the Spanish government. But the bulk of the guns remained in inventory or storage until 1951, when the West German Police adopted the gun, and bought everything Astra still had (45,350 approximately). These were later amalgamated into the Bundeswehr inventory in 1956, before being replaced by the Walther P1 in 1961.