Hispano-Suiza HS.404, 20&time;110mmHS (France, 1938)
Designed by Swiss engineer Marc Birkigt, who was seeking to improve on the Oerlikon Typ S (GURPS High-Tech, p. 132). The HS.404 uses a gas-unlocked delayed-blowback operating mechanism and feeds from 60-round drums. Originally intended for mounting on top of a fighter plane engine, it was adapted for both aircraft and anti-air use. It suffers from frequent issues with light strikes failing to ignite primers, which can be a serious problem in aircraft mountings where it may not be possible to eject a dud round. It also had issues extracting spent casings, requiring the ammunition to be lubricated.
Following the fall of France, production shifted to the company’s Swiss factory, where it was named the HS.804. A 160-round drum (180 lbs. loaded, 89 lbs. empty, $1,000) was developed for anti-aircraft use, although this suffered from feeding problems unless underloaded (GURPS Tactical Shooting, p. 20).
The British had licensed the design from the French and produced it as the Hispano Mk I. They further developed the design by shortening the chamber to reduce the chance of light strikes, and switched to a belt feed system. The resulting weapon was known as the Hispano Mk II. A final refinement lightened the gun and fluted the chamber to overcome extraction issues, designated the Hispano Mk V. The HS804 produced by British firm AEI systems is functionally very similar to the Hispano Mk V.
In America, a belt-fed version known as the AN-M2 was designed for the US Army and Navy. This failed to resolve the reliability issues, and the subsequent M3 was only marginally better. A version of the M3 with an electric firing and cocking mechanism was designated M24 and used in aircraft turrets. Old M3s and M24s were modified for use as deck guns in the 1960s, designated Mk 16 Mod 4 and Mod 5 respectively.
The first HE shells developed for the HS.404 had overly sensitive fuzes, causing them to explode before penetrating the target (Dmg 2d [1d] cr ex), so ball rounds (in table) were issued instead. An improved HE round (Dmg 6d×3(0.5) pi++ with a 2d [1d] cr ex follow-up) became available in 1941. Other commonly used rounds include AP-T (Dmg 6d×2(2) pi+), APHC (Dmg 6d×3(2) pi+), and SAPHE (Dmg 6d×3) pi++ with a 2d [1d] cr ex follow-up).
GUNNER (MACHINE GUN) (DX−4 or other Gunner at −4)
| TL | Weapon | Damage | Acc | Range | Weight | RoF | Shots | ST | Bulk | Rcl | Cost | LC | Notes |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 6 | HS.404, 20×110HS | 6d×3 pi++ | 5 | 1,900/7,200 | 110/56 | 11! | 60(5) | 27M† | −11 | 4 | $20,000/$500 | 1 | [1] |
| 7 | Hispano Mk II, 20×110HS | 6d×3 pi++ | 5 | 1,900/7,200 | 101/82 | 10! | 120(5) | 26M† | −11 | 4 | $20,000 | 1 | |
| 7 | Hispano Mk V, 20×110HS | 6d×3 pi++ | 5 | 1,900/6,900 | 101/82 | 12! | 120(5) | 26M† | −10 | 4 | $20,000 | 1 | [2] |
| 7 | AN-M2, 20×110HS | 6d×3 pi++ | 5 | 1,900/7,200 | 132/82 | 11! | 120(5) | 26M† | −11 | 3 | $20,000 | 1 | [1] |
| 7 | M3, 20×110HS | 6d×3 pi++ | 5 | 1,900/7,200 | 116/82 | 12! | 120(5) | 27M† | −10 | 4 | $20,000 | 1 |
[1] Unreliable. Malfunctions on 16+.
[2] Very Reliable. Won't malfunction unless Malf is reduced.