In the Second World War the objective was to equip each ship with a low-angle gun mounted aft as defence against surfaced submarines and a high-angle gun and rifle-calibre machine guns for defence against air attack. 3,400 ships had been armed by the end of 1940 and all ships were armed by 1943.
https://en.wikipedia.org/wiki/Defens..._merchant_ship
The armament is in the ship.eqp file with the date of delivery of the corresponding armament. Edit. as you yourself think is right.