To: Chief of Staff of the Navy Adm. Jacinto Pablo Peablo
Defence Minister Vice Adm (ret). Juan Perez Benedicto Hood
MR/T172/34
TOP SECRET
Lessons of Riverine Operations and Future Requirements
Armament: The 155mm and 75mm guns fitted (standard army guns on naval mounts) have proved satisfactory in service. Powerful artillery able to silence most fortifications and suitable for counter-battery work. 75mm can also fire useful AP shot.
The use of standard Italian pattern 37mm AA guns will increase to provide rapid fire able to break up most infantry attacks and disable other river vessels built of wood or light metals. AP shot will also be provided. 20mm cannon will supersede 13mm Browning HMGs for anti-air and anti-infantry roles. More 81mm mortars for support missions are needed when they become available. Boats armed with heavy and light weapons are required to support each other as both have different tasks and both cannot be done satisfactorily in one hull.
Propulsion: Diesels are preferable but wood burning boilers may prove useful for smaller patrol craft. Petrol engines will not be used because of the fire risk.
CLASSES
Motor Gunboats
Type 1A River Gunboat (wood) 19 tons, 17.5/3.2/0.6m, two 150bhp diesels 12kts, 2x20mm 4x7.92mm MG, 12 crew. A useful patrol design but limited attack ability but capable of destroying light river craft.
Type 3A River Gunboat (wood + steel) 27 tons, 19/4.8/0.6m, two 150bhp diesels 11kts, 1x37mm 1x20mm 3x7.92mm MG, 19 crew. An enlarged Type 1A with 37mm cannon, still under armed but still a useful armament for patrol duties.
Project 612 Type 6A (Italian MZ1) transport with bow ramp (3x20mm), B supply/tender for MTB (1x37mm 3x20mm) and C fire support (1x75mm M1931 1x 37mm 2x20mm 4x7.92mm MG 4x81mm mortars). Transport for Marines for assault and general transport duties, one supply tender variant will be issued to each MTB/MGB squadron by 1940. The fire support variant may be replaced by Project 611 boats but it offers great firepower in the attacking role, not so useful for defence.
Type 7A River Gunboat (wood + steel) 27 tons, 19.2/4.8/0.65m, two 150bhp diesels 11kts, 2x37mm 2x13mm HMG 2x7.92mm MG, 21 crew. Planned improved Type 3A with two 37mm cannon.
Gunboats
Parana Class: Badly in need of updating or replacement. Parana now in drydock will be rebuilt with modern diesel engines and standard Army 155mm and 75mm guns to bring her up to a modern standard. Rosario unlikely to be refitted but replaced (see below)
Patria: Awaiting surveyors report to establish if economic repairs can be carried out. If not plans for two replacement gunboats (Project 614) have been made equal in firepower to the Los Andes Class but with deck and belt armour sufficient to defeat light AP and HE projectiles.
Los Andes Class: Modern and immensely powerful with four 155mm guns and three 75mm guns but no armour makes these vessels vulnerable to mortar and artillery attack.
Chaco Class: Planned gunboat variant cancelled.
Project 611: Two new Squadrons to be formed with a mix of types. Each will have three 611L2 and three 611L3 boats. The 611L2 is armed with two 75mm guns with armour around the bridge; these will support the 611L3 with three 37mm mounts of undecided type with similar armour.
We are short of capable craft for patrol missions with the necessary firepower and the Committee recommends replacement boats are acquired as soon as possible to augment the gunboat fleet while new construction takes place. Funds are requested from the 1933 Destroyer Class to enable these plans to reach fruition sooner because of the immediate tactical need of this branch of the Navy to support the Army's operations.