In Part 7 of our series on the Falklands War, I mentioned the SS Canberra being put into service as a troopship, and mentioned that this was different than being an attack transport for amphibious warfare. So, Roamy asked me, “What’s the difference?”
In the days before jet airliners, if you wanted to move a lot of people overseas, your only option was to use a ship. Consider the US Army gearing up for the invasion of France. The Army crammed a million or so soldiers into England in preparation of the invasion, not to mention the hundreds of thousands of ground support troops needed by the Army Air Forces there.
To get those troops to England, the Navy (and the Army) used troopships, ships with the designation “AP” for Auxiliary (as opposed to a warship) Transport. Troop transports were intended to move the largest number of troops from one port to another. They didn’t carry equipment, vehicles or supplies, and were intended to be unloaded at modern port facilities.
Unit integrity was not a critical factor in the employment of troopships. If a transport had berthing for 3,040 bodies, then 3,040 bodies would be loaded up, no matter which units those warm bodies came from. Everyone would get sorted out after arriving at the destination, they’d marry up with their equipment (which was transported separately on cargo ships) and then get ready to move out.
Troopships were typically either passenger liners converted to the role, or ships built to modified passenger liner design.
The Army actually operated its own fleet of transports for several years. Crewed by civilians, these Army owned ships moved troops around the world. Eventually, the Navy sought and gained control of all major shipping under the Military Sea Transportation Service (MSTS). The ships were still crewed by civilians, and still supported Army movements, but were administered and scheduled by the Navy.
A typical troop transport would be the USS General M. C. Meigs, AP-116, later transferred to MSTS and redesignated T-AP-116 US Naval Ship General M. C. Meigs. The change in designation reflected that she was no longer a commissioned ship of the Navy, and instead was operated by MSTS. A sister ship is pictured below.
Attack transports, while looking much like transports, were actually a fundamentally different design with an entirely different operational concept.
Attack Transport, known as APAs, were intended to embark a complete military unit, typically a battalion, a portion of its vehicles, and its initial supplies of ammunition, fuel, food and water, move them to the objective, and launch them directly into an amphibious assault using its own embarked landing craft.
APAs were based on cargo vessel designs, rather than passenger liners. Cargo holds were needed for unit vehicles and supplies, and the cargo handling booms were needed to launch embarked landing craft such as LCVPs and LCMs, and then load them with cargo. Troop berthing space was created by converting some of a ships cargo holds to berthing and messing spaces.
A typical attack transport was the Bayfield class built during World War II.
Attack transports were “combat loaded.” That is, the vehicles and equipment aboard was stowed based upon the order in which things needed to be unloaded first. This is the least efficient use of space, but obviously, in an amphibious assault, getting the order unloading is a greater priority than maximum use of available space.
Ideally, each APA would carry enough of its own landing craft to land all the assault elements of its embarked battalion in one wave. Once the landing craft had landed the troops, they would return to the ship to load supplies and the support elements of the battalion. The attack cargo ship, or AKA was very similar, but was geared more to carrying the extra vehicles and follow-on supplies to the assault.
Unloading quickly was very important. First, the sooner everyone was ashore, the more weight and momentum a landing would have. Second, the sooner the ships were empty, the sooner they could leave the area, before enemy air or submarines could launch counterattacks. When R. K. Turner withdrew the attack transports from Guadalcanal before they finished unloading (he was facing a possible heavy Japanese counterattack by cruisers that night), the Marines ashore were left with a very shaky logistical foundation upon which to build their campaign.
The Navy eventually bought or built several hundred attack transports during World War II. And many remained in service for decades after the war. The last APA in the US Navy was decommissioned in 1970. Their role in landing the assault waves had been taken over by other, more specialized designs such as the helicopter landing ship (LPH) and landing ship, personnel, dock (LPD).
As noted above and in Part 7, the SS Canberra was used as a troopship. But in this instance, there were some differences in the way she was employed. The Brits loaded her with a close eye to unit integrity. Secondly, it was not intended that she disembark her troops in port. Rather, after the amphibious warfare ships such as the Roundtable class had made their first landings, they would shuttle back to the Canberra and other liners, reload with more troops, and make followup landings. In effect, the units involved had to do the reorganization and reloading normally done at a port of embarkation on the open seas. It wasn’t an optimum solution, but few things in war ever lend themselves to that.
Of course, anyone wanting to explore this further, and lighten their wallet by a bit, should check out US Amphibious Ships and Craft.