If one were to use a half unit pump can they make the 3 units into 2 1.5 unit cannons? I am not sure since the rule does not state anything like this. But it really is not breaking the spirit of the rule or I would think. The only thing it mayb skirting is the bolded portion and I am not sure. But then again if this is true I guess a 5 unit ship could have a 1.5 haymaker and sterngun with a one unit bow side mount. Maybe I am opening a can of worms and just answered my question..
5. A one unit cannon carries a load of 50 bbs fired singleshot, or 15 bbs if spurted. A 1/2 unit cannon carries 25 bbs fired singleshot, or 10 bbs if spurted. A 1/2 unit cannon magazine may be added to a 1 unit cannon magazine, making a 1 1/2 unit cannon with 75 bbs. Cannon units may not be subdivided into smaller cannon units (a 1 unit cannon may not be made into two 1/2 unit cannons). A ship may mount only a single ½ unit cannon in its offensive armament. In Ship Classes 3 and above, any legal 1/2 units must be used as a cannon with 75 bbs in the magazine. Only Class ½, 1, 2 and 3 ships with all cannons in the bow and/or stern quadrants may be armed with spurt cannons.
The reason I ask this is because while I am making ally ships now. One day I will make a Tegetthoff class DN (I just love the look of her and her sister ships) and cruiser to accompany it.. I may just make it easy and do a Graff Spee since I loved it as a kid.