Yours is possibly the broadest question I have attempted to answer. Without weapons, NO war is possible. At sea, the submarine was greatly improved from WW1. Surface vessels had greater range and speed. The aircraft carrier pretty much meant the end of the battleship. On land, artillery, rifles and machineguns were similar to WW1, but the tank was greatly improved in speed, mobility and firepower. In the air, guided missiles were used effectively against cities. Fighters with greater speed and range provided defense, and bombers could destroy cities. The ultimate weapon- the atomic bomb- ended the war.