Vessels and underwater craft form this subject group, and one rule outranks all the others at sea: scale decides everything. The prototype is tens or hundreds of metres long, so even a small scale leaves you with a model past half a metre. Measure the shelf before you buy, not afterwards.
Surface ships and submarines then pull in opposite directions. A warship lives on superstructure, armament and railings; a submarine is simple in outline and all the work goes into a hull that must end up without a visible seam anywhere along it. The arithmetic is worth doing before the order: a 263-metre battleship comes out at 75 centimetres in 1:350, and a 67-metre submarine at 93 centimetres in 1:72. Surface vessels, sorted so the finished length follows from the scale, are in ship model kits, and underwater craft in submarine model kits.
