In the largest part of the navies the development of patrol boats and fast craft took place fundamentally during the 1930s, increasing
their size and armament during the subsequent war. It was particularly notable the quality of the German boats which were known by the Allies as "E-boats",
or simply as the enemy boats par excellence, without further distinction from other enemy types. In the end, they resulted not so effective against
the British counterparts in the North Sea as it had been expected. However this fact has been mostly attributed to a notable lack of aggressivity in the German
command and not to the design of the boats.
As the largest part of the postwar navies of the Baltic countries, the Swedish Navy comprised mainly a large number of small submarines and fast boats.
The harsh waters, the numerous isles existing in the vicinity of the coasts and the great amount of land airbases on the region put the Swedish
defensive primacy on high speed units and an effective antiaircraft armament. Sweden deployed from the 1960s six units of the Spica class armed with six
torpedo tubes and an automatic 57-millimeter antiaircraft cannon of high rate of fire.
The category of patrol boats is composed as well by units not equipped with torpedoes, and the most modern ones are equipped with missiles, albeit the
cannon remains as a fundamental piece in every boat of this type. According to the artillery embarked, the classic patrol boats could be classified as
heavy or light types. In any case, they usually carried several pieces featuring a diversity of calibers for a better flexibility of fire, allowing to
destroy both surface and aerial targets. A good example are the patrol boats designed by the German company Lurssen for the Spanish Navy in the 1970s.
British patrol torpedo boat of the Vosper 70 class (1939-1942)
German patrol torpedo boat Schnellboot S-80 (1942)
Swedish patrol torpedo boat of the Spica I class circa 1970