For All Nails #154: Necessity is the Mother Of...
by Bernard Guerrero
- From Thomas Cochrane's Fighting Ships, 30th Edition, Copyright 1970
- Cochrane Naval Press, Annapolis, Maryland, N.C., CNA
"...In mid 1943, the NUSM Puerto Hancock design bureau was tasked with the development of a company-strength submersible troop transport. It was already becoming apparent as early as 1942 to operational-level echelons in Siberia that maintaining air-superiority over broad swaths of the continental front-lines, the littoral and Japan itself was becoming an ever more difficult task, making the small scale amphibious strikes in use as an operational flanking technique a dicey proposition at best. Still, amphibious operations were seen as a strategic sideshow and it seems likely that the concerns of local commanders would never have advanced as far as Chapultepec Castle had it not been for serendipity. At Silva's prompting, concepts for a "knockout blow" against Japan were being floated during this period, and planners seized on the idea of submarine transport as a hedge against the increasingly strong Japanese presence in the air over the Home Islands.
The original 1942 design concept of a mid-range diesel-electric of about 3,000 tons displacement (already a fairly large boat) capable of delivering a company of marines was transformed into the Sirena-class, 6,500 ton surface-displacement monstrosities capable of delivering a battalion of heavy infantry along with motorized transport or, as the Conquistador sub-class, an armored company of 12 terramobiles. Range was cut to a bare minimum as the boats were optimized for the Siberia-Japan crossing. The troops and vehicles would be unloaded over a bow ramp, coming under the support of 4 bow-mounted .50 caliber autocannons.
Nine Sirenas and three Conquistadors were completed in time for the invasion of Honshu in 1944, and all participated. Hippocampo was lost on approach to Honshu with all hands due to a magnetic mine, but the eleven other craft delivered their charges, achieving complete operational surprise.
The Sirenas continued in use in-theater for the duration of the Mexican presence, used first to ferry troops and supplies to Japan under the increasingly effective Imperial Japanese Air Arm and then later during the evacuation of Mexican and Siberian troops from the collapsing position. It was during the final days of the pocket's existence that the Sirena herself was lost, coming under dive-bomber attack as she was on-loading elements of the 132nd Infantry Regiment for the return trip to Siberia. This effectively signaled the end of the organized evacuation as it became impossible for the NUSM to approach the Japanese coast in any meaningful way.
The remaining Sirenas were retrofitted for longer range operations and spent the rest of the war in use, dispersed across the Pacific, evacuating marines here and delivering a final load of supplies there.
Post-war, the entire class were deemed surplus to the operational needs of the NUSM and were transferred to the AFANG en masse in 1960 with the exception of Cochise and Grifo, which were refitted as technology test-beds."
Forward to FAN #155 (Global War): Welcome to the Jungle.
Forward to 1970: These Are the Journeys.
Return to For All Nails.