The HS.404 cannon is broadly similar to the contemporary Oerlikon cannon, though they are not mechanically related. An aircraft version of the HS.404 was developed at the request of the French in 1938, and equipped many of their aircraft, including mounted firing through the propeller hub in fighters such as the MS.406 and VG.33. The British also adopted it as the Hispano Mk I, however numerous reliability issues took time to work out, and it was developed into a belt-fed version, the Hispano Mk II in 1941. After the gun's teething issues were sorted, the Hispano became a staple of British aircraft weaponry during WWII. The short-barrel, higher rate of fire Hispano Mk V was developed later in the war.
The Americans had somewhat more trouble getting the cannon to work. They adopted the equivalent to the Hispano Mk I as the 20mm AN/M1 which saw little use, then created the 20mm AN/M2 (not to be confused with the .50 AN/M2 or .30 AN/M2) using the Hispano Mk II as reference, but this version still had reliability issues; it was most notably equipped on the P-38 Lightning, where the plane's unique layout allowed for a manual recocking lever, making the seemingly inevitable malfunctions less of an issue. The 20mm AN/M3 (not to be confused with the .50 AN/M3) was the equivalent to the Hispano Mk V, with a post-war upgrade that added electrical recocking designated M24.
Other countries also built or used their own variations of the HS.404 during this time period, usually copies/iterations of the British designs; Sweden was a notable example.
The Hispano-Suiza HS.404 appears in the following films and video games used by the following actors:
