Casualties and injuries are almost always apparent in war, not to mention diseases and illnesses that can occur in hostile environments such as thick forests, isolated islands, and the middle of the ocean. Yet, for American troops deployed in the Asiatic-Pacific Theater during the Second World War, it was almost impossible to access immediate medical care, particularly on island battlefields that were hot, rainy, and riddled with mosquito-borne illnesses like malaria and yellow fever. Not exactly ideal places for a hospital ashore. This is where hospital ships come in together with evacuation ships, aka floating ambulances of the American forces that would provide medical support and ferry incapacitated men into safety. Mostly slightly smaller than hospital vessels, evacuation ships rose to prominence notably at the end of World War II, when they delivered men home.

So, what was the difference between a Hospital ship and an Evacuation ship? It all came down to the Geneva Convention. You see, hospital ships are clearly marked and painted white for easy identification.  During the war, both sides would give notice that hospital ships were operating in an area. These were generally respected by the Germans, but not by the Japanese. The US evacuated casualties to England, the US, and Hawaii for treatment and recovery, but realized that having dozens of purpose-built hospital ships meant they would be building fewer troop transports which were desperately needed as well.  And all these hospital ships would be making the return trip to the war zone empty and would be away for weeks. They were also very slow-moving vessels.  They could not transport troops or supplies lest they become targets of attack. So while the navy and army built Hospital ships to initially treat the wounded, the navy undertook the additional step of creating purpose-built Evacuation ships that could be armed and be able to make the return trip with troops and supplies for the vast reaches of the Pacific front. Of course, this made them legitimate targets for attack by enemy forces, so the military made sure that the wounded placed aboard them were ‘ambulatory,’ meaning that they could get around on their own and be able to man life rafts and boats if the ship was bombed or torpedoed on the way home.

These ships also had to be able to reconfigure for the return journey for troops and cargo. While the bunks for medical evacuation missions were only stacked two high to allow doctors and nurses to treat their patients on the trip to the states, this limited the number of patients they could carry to about 600. On the return trip, the bunks might go five high and now the ship was able to carry 1,500 troops back to the front in the Pacific. They also had to be fast, relatively speaking. While the Liberty ships that moved most of the troops and cargo across the Pacific and Atlantic oceans moved at a leisurely and fuel efficient 12 knots, the Evacuation ships could do 18 knots which were very fast for transports ships of that time. This would help them outrun any submarines trying to stalk them and allow them to travel without escorting destroyers.

The Army would build some 24 Hospital ships during WWII, while the Navy would build 15 Hospital ships, but just 3 Hospital Evacuation Transports were ever built.

Check out the 3 Hospital Evacuation ships that rose to the occasion in WWII.

USS Tryon (APH-1)

SS Alcoa Carrier had her keel first laid down under the Maritime Commission contract in mid-March 1941 at Oakland, California. She will eventually be renamed Comfort in June 1942 and Tryon (named after Commodore James R. Tryon, a USN medical doctor) in August 1942, before the Navy procured and commissioned her to service in September 1942 under the USN Commander Alfred Jensen Byrholdt.

Evacuation Ship USS Tryon
After an unsatisfactory overhaul, USS Tryon (APH-1) set anchored off San Francisco circa 1945. (Image source: Navsource)

A purpose-built evacuation ship, the USS Tryon, was sent to join the Service Squadron during the Asiatic-Pacific Theater and, for the next 15 months, evacuated combat casualties from the Solomons to Suva Noumea, Wellington, Auckland, and Brisbane. Around this time, the Second Geneva Convention was yet to be signed. So, aside from transporting the sick and wounded, Tyron also engaged in combat duties. After the Second World War ended, USS Tryon was assigned to Operation Magic Carpet, a fleet mission to bring hundreds of thousands of US troops home from the war.

Over a month after transporting the last batch of returning soldiers, she was decommissioned at Seattle. She remained inactive before being transferred to the US Army in July 1946, which converted her into a troop transport under the new name USAT Sgt. Charles E. Mower. She was handed back to the Navy in 1950 and was used to shuttle dozens of soldiers from San Francisco to Pearl Harbor until her relieved of duty on 1954.