Here is another example of a converted merchant ship into military troop transport:
Armament:
4x 15 cm/50 41st Year Type guns
2x 8 cm/40 3rd Year Type naval guns
2x 4 Type 93 13.2-mm machine guns
2x 4 533 mm (21.0 in) torpedo tubes
As a military transport
From 16 December 1942, Aikoku Maru was reassigned back to the IJN 8th Fleet, primarily as a military transport to support New Guinea operations, and her aircraft were disembarked. While unloading cargo at Madang on 18 December, she was attacked in an air raid by B-17 Flying Fortress bombers of the 43rd Bomb Group of the USAAF Fifth Air Force, but was not hit. She returned to Kure on 29 December 1942.[1]
As part of “Operation C” (the Reinforcement of New Guinea), on 5 January 1943, Aikoku Maru loaded the IJAAF 209th Airfield Battalion, 14th Aerial Repair Shop and others, a total of 691 men plus 34 vehicles at Pusan in Korea, arriving at Rabaul on 14 January. She was then sent to Tsingtao in Japanese-occupied China, arriving 24 January, and from there to Cebu (2 February) and Palau (7 February), where she loaded additional troops and cargo, delivering the reinforcements successfully to Wewak on 23 February. She returned to Kure on 5 April.[1]
On 10 July 1943, as part of a convoy including the aircraft carrier Un’yō, Aokoku Maru was attacked by the submarine USS Halibut 170 nautical miles (310 km; 200 mi) north of Truk, which fired six torpedoes. One struck Aikoku Maru, causing moderate damage. On her return voyage, on 15 July, she was attacked again, this time by the submarine USS Tinosa, whose four torpedoes all missed. She returned to Kure on 2 September.[1]
On 6 October, Aikoku Maru returned to Tamano for repairs and refitting with additional weaponry, which included two 152 mm guns and four twin-mount Type 96s. The refitting work was completed by 31 December 1943.
https://en.wikipedia.org/wiki/Aikoku_Maru_(1940)
Armament:
4x 14 cm/50 3rd Year Type naval guns,
2 Type 93 13.2-mm machine guns
2x 4 533 mm (21.0 in) torpedo tubes
Military service
On 6 August 1941, Kongō Maru was requisitioned by the Imperial Japanese Navy and was converted to an armed merchant cruiser at the Harima Shipyards at Aioi. Single mount 14 cm/50 3rd Year Type naval guns were installed at her bow and stern, as were two Type 93 13.2-mm machine guns and two 533 mm (21.0 in) torpedo tubes. Her conversion was completed on 14 October and she was assigned to the IJN 4th Fleets South Seas Force and deployed to Truk. At the time of the attack on Pearl Harbor, Kongō Maru was at Kwajalein, from which she deployed as part of the Japanese task force in the first attempt to invade Wake Island on 8 December 1941. She was bombed by USMC F4F Wildcat aircraft using depth charges, and caught fire. The fires were brought under control and she returned to Kwajalein. She later participated in the second attack on Wake Island on 21 December 1941, which succeeded in taking the island. After the battle, Kongō Maru was sent via Saipan, Truk and Guam to participate in the battle of Rabaul on 22 January 1942.[2]
During the invasion of Lae-Salamaua on 8 March 1942, Kongō Maru transported elements of the Japanese Special Naval Landing Forces to Huon Gulf in what is now eastern Papua-New Guinea. While still at Huon Gulf of 10 March 1942, Kongō Maru was bombed and sunk by aircraft from the United States Navy aircraft carriers USS Lexington and USS Yorktown at 06 49′S 147 02′E.[2] She was removed from the navy list on 20 March 1942.
https://en.wikipedia.org/wiki/Kongō_Maru_(1935)
If Transport are considered Troopships, it seems very dumb to not trying to give some Air defense to protect the costly soldiers which take a lot of time to replace.
I can understand that cargo ships were less important, stock can be rebuilt faster.
A functional military unit cannot be rebuilt that fast. Training take times.
I see no absolute reason to treat Transport unit as only merchant ship.
And, on the reverse, there is no absolute reason to not consider Transport unit as military troopship.
The game does not actually consider fuel, supplies, drugs, cloths, food and shelters shipping on the map.
Even G40, the more complex and detailed game, get a special Convoy Disruption rule to consider the economic aspect and impact on merchant shipping.