Prior to World War II, the fleet renewal program led to the acquisition or construction of five submarines, four torpedo boats, and two coastal defense ships. Among the last of their kind, and "Ilmarinen" were two of the most concentrated naval artillery units ever built. They were designed by the Dutch company NV Ingenieurskantoor voor Scheepsbouw (a front for German interests circumventing the Treaty of Versailles), and were optimized for operations in the archipelagos of the Baltic Sea. Their open sea performance was de-emphasized in order to give the vessels their shallow draft and super-compact design.