An extract on #marines
Historically, tasks undertaken by marines have included: helping maintain discipline and order aboard the ship (reflecting the pressed nature of the ships' company and the risk of mutiny), the boarding of vessels during combat or capture of prize ships, and providing manpower for raiding ashore in support of the naval objectives.
With the industrialization of warfare in the 20th century the scale of landing operations increased; this brought with it an increased likelihood of opposition and a need for co-ordination of various military elements. Marine forces evolved to specialize in the skills and capabilities required for amphibious warfare.
In the earliest day of naval warfare, there was little distinction between sailors and soldiers on a warship. The oarsmen of Ancient Greek and Roman ships had to be capable of fighting the rowers of opposing ships hand-to-hand; though hoplites began appearing on Greek ships specifically for the boarding of enemy ships. The Romans were the first to understand the importance of professional soldiers on board of ships. Since during the first punic war Roman crews remained inferior in naval experience to the Carthaginians, and could not hope to match them in naval tactics, which required great maneuverability and experience. They therefore employed a novel weapon which transformed sea warfare to their advantage. They equipped their ships with the corvus, possibly developed earlier by the Syracusans against the Athenians. This was a long plank with a spike for hooking onto enemy ships. Using it as a boarding bridge, marines were able to board an enemy ship, transforming sea combat into a version of land combat, where the Roman legionaries had the upper hand. During the early Principate, a ship's crew, regardless of its size, was organized as a centuria. Crewmen could sign on as marines (Called Marinus), rowers/seamen, craftsmen and various other jobs, though all personnel serving in the imperial fleet were classed as milites ("soldiers"), regardless of their function; only when differentiation with the army was required, were the adjectives classiarius or classicus added. The Roman Navy's two fleet legions, I Adiutrix and II Adiutrix, were among the first distinct naval infantry units .
The first organized corp of marines was created in Venice by the Doge Enrico Dandolo when he created the first regiment of ten companies spread on several ships. That Corp participated to the conquest of Byzantium (1203-1204), later officially called " Fanti da Mar" ( sea infantry ) in 1550. Later also the Spanish king, Carlos I, assigned the naval infantry of the Compaas Viejas del Mar de Npoles (Naples Sea Old Companies) to the Escuadras de Galeras del Mediterrneo (Mediterranean Galley Squadrons) in 1537, progenitors of the current Spanish Navy Marines (Infantera de Marina) corps. The third oldest marine corps in the world was founded as the Tero of the Navy of the Crown of Portugal in 1618, predecessor to the modern Portuguese Marine Corps.