The pistol was mass-produced and many examples still exist today. The Spanish Navy, along with the German Luftwaffe and the Chilean Navy primarily use the smaller variant Astra 300 and the Wehrmacht later altered the Astra 400 into the Astra 600 to better handle the 9mm Luger. The 400 was considered heavy as in order to handle the power of the 9mm Largo round in a blowback action the 400 had a reinforced slide and tough spring.
The Astra modelo 400 was a Spanish service pistol produced by weapons manufacturer Astra-Unceta y Cía SA. as a replacement for the Campo-Giro 1913/1916, which had also been chambered in 9mm Largo. It was the standard issue sidearm in the Spanish Army during the Spanish Civil War and also saw service in Germany during World War II.
The Spanish War Ministry of King Alfonso XIII began tests in 1919 to replace the Campo Giro pistol as the standard military sidearm. The 9mm Largo Astra modelo 400, patented by Pedro Careaga, was selected for the Spanish Army in August 1921, and was also adopted by other Spanish Armed forces. Astra pistols were supplied to Republican Spain and to the Basque government which controlled the plant until the Bombing of Guernica in April, 1937. Astra pistols were subsequently produced for Nationalist troops, while Republican forces made approximately 22,000 copies of the pistol in Terrassa (marked F. Ascaso) and Valencia (marked RE for Republica Española). Astra production after the civil war was for Nationalist troops except serial numbers 92851 to 98850 for Nazi Germany. Astra continued private production until 1950 even though in 1946 the Spanish military adopted the Star Model A as the standard sidearm. Spanish military inventories were sold to civilian wholesalers between 1956 and 1965. A total of around 106,175 pistols were produced.
The Astra 400 is heavy compared to many contemporary service pistols of the time like the Tokarev TT-33 but is similar in weight and length to the Colt 1911. The Astra 400 was designed to be safe to fire with a simple blowback action unaided by any breech-locking devices. This is only possible with a heavy slide and strong recoil spring. It was fitted with an internal hammer which was considered very hard to cock. The pistol also featured grooved finger grips and left sided trigger catch behind the trigger guard. The original design was chambered in 9mm Largo, but later variants would be chambered differently so as to better fulfill different military needs.