When I put one battleship in the shipyard build queue the production time is 1 turn.

If I add two battleships in shipyard build queue the construction time is 1 turn for the first battleship and 5 turns for the second battleship.

The military value in my shipyard is 140.7 the battleship has construction cost 700. Not sure why if I only add one battleship in the build queue my production time is 1 turn. I could just keep only putting 1 ship in the queue and make ships faster.

Seems like the production time is calculated wrong. Why is it not 5 turn production time all the time??