A slightly improved version of the 100 mm/47 Model 1928 specifically intended for submarines but also used on a few auxiliary vessels. Manufactured by OTO. Slightly shorter than the other 100 mm/47 guns.
| Designation | 100 mm/47 (3.9") Models 1931, 1935 and 1938 for Submarines |
|---|---|
| Ship Class Used On | Glauco, Marcello, Cappellini, Liuzzi, Marconi, Cagni, Sirena, Perla, Adua, Argo, Acciaio and Flutto classes Foca and Brin classes as rearmed |
| Date of Design | 1931, 1935 and 1938 |
| Date In Service | 1932 |
| Gun Weight | N/A |
| Gun Length oa | 194.5 in (4.940 m) |
| Bore Length | N/A |
| Rifling Length | N/A |
| Grooves | N/A |
| Lands | N/A |
| Twist | N/A |
| Chamber Volume | 473.5 in3 (68.79 dm3) |
| Rate Of Fire | 8 - 10 rounds per minute |
| Type | Fixed |
|---|---|
| Complete Round Weight | N/A |
| Projectile Types and Weights | HE: 30.4 lbs. (13.8 kg) |
| Bursting Charge | N/A |
| Projectile Length | N/A |
| Propellant Charge | N/A |
| Muzzle Velocity | 2,756 fps (840 mps) |
| Working Pressure | N/A |
| Approximate Barrel Life | N/A |
| Ammunition stowage per gun | N/A |
| Designation |
|
|---|---|
| Weight | 4.6 tons (4.7 mt) |
| Elevation | OTO 1932: -5 / +32 degrees Others: -5 (?) / +35 degrees |
| Elevation Rate | Manually operated, only |
| Train | 360 degrees |
| Train Rate | Manually operated, only |
| Gun recoil | N/A |
All submarines carried one of these guns.



Data from:
- "Naval Weapons of World War Two" by John Campbell
- "Italian Warships of World War II" by Aldo Fraccaroli
- "Marconi Class Submarines at War" article by Pierre Hervieux in Warships Volume VIII
- 07 December 2007
- Benchmark
- 23 September 2012
- Added picture of museum gun
