O-21-class Submarine
The Dutch O-21 class patrol submarines were designed for use in other than European waters and were considered among the best submarines of there type when launched. Most had not been completely fitted out when Germany invaded in 1940. However, four of the subs (O-21 to O-24) were able to reach England. A fifth boat (the O-25) was scuttled but later raised and completed by the Germans (the other three boats were also finished by the Germans).
The boats included snorkel gear, but the British considered it ineffective and unsafe and it was removed from the O-21 and O-22. The four Allied boats were active during the war, under British command but with Dutch crews. The O-22 was sunk in November 1940, but the O-21, O-23 and O-24 (along with the O-27, returned by Germany after the war) survived into the 1950’s.
The O-21 has a crew of 39. It mounts four 21” torpedo tubes both fore and aft. An 8.8cm AA gun is carried on the afterdeck. The engines burn 155 gallons of diesel fuel per hour of routine usage. The O-21 can travel 11,500 miles at 13 mph surfaced and 32 miles at 10 mph submerged.
O-21
Subassemblies: Medium Corvette chassis with Sub option
+8; sealed Medium Secondary superstructure [Body:T] +3; full-rotation Small
AFV open mount.
Powertrain: 2¥1,940-kW marine diesel engines with
2¥1,940-kW water screws and 62,000-gallon standard tanks; 2¥373-kW
electric motors with 9.72 million-kWs batteries†.
Occupancy: 23 CS Body, 5 CS Sup Cargo:
793 Body, 117 Sup, 3 OM
Armor
Body: 4/55
Sup: 4/55
OM: 0/0
Weaponry
4¥533mm Torpedo Tubes [Body: F] (*).
4¥533mm Torpedo Tubes [Body: B] (*).
88mm Med. Tank Gun [OM:F] (200).
* Fourteen torpedoes are carried.
Equipment
Body: Autopilot; backup driver controls; 1,900-VSP bilge; 15¥bilge
pumps†; 20¥bunks; 100-VSP cargo holds; 50-man environmental control†;
12¥fire extinguishers†; 40-man-days life support†; navigation instruments;
precision navigation instruments; 5130-man/days of provisions; 2-mile passive
sonar. Sup: Navigation instruments; 1¥20’ 15¥ periscopes;
2¥very large radio receivers and transmitters; searchlight. OM:
Universal mount.
† Limited access.
Statistics
| Size: 255’¥22’¥45’ | Payload: 268 tons | Lwt: 940 tons |
| Volume: 8,165 | Maint.: 9 hours | Price: $449,000 |
HT: 10
HP: 51,000 [Body], 750 [Superstructure], 150 [Open Mount]
| wSpeed: 22 | gAccel: 0.1 | gDecel: 0.5(0.6) | gMR: 0.05 | gSR: 4 | Draft: 13' |
| uSpeed: 10 | gAccel: 0.05 | gDecel: 0.3(0.4) | gMR: 0.05 | gSR: 4 | uDraft: 45' |
Design Notes
The 1,205-ton historical submerged weight was used for underwater performance
calculations. Design wSpeed was 19 mph and uSpeed was 8mph; the historical
figures were used instead.
A 12.7mm AA gun (Very Long Ground HMG) was frequently carried on a pintle mount on the conning tower.
Variants
The O-16 (1936) was a slightly smaller boat. It was about 2mph slower
on the surface and had two extra 533mm tubes in a rotating mount and a
pair of 40mm AA guns in retractable tubs. The O-16 ran into a British minefield
in the Pacific and sank in December of 1941.
There is some confusion over what armaments the other boats carried. The O-22 to O-24 probably were the same as the O-21. The three boats used by the Germans (including the O-25, which had been scuttled but then raised) probably mounted 20mm AA guns.