To the question of where the 400-ton corsairs come from: why not make them
privateers instead of pirates? I know this is going a little beyond what a
privateer is normally defined as, but the corsairs are built by empires
hostile to the Imperium, and, in exchange for a share fof the loot, and a
promise not to attack *that* empire's shipping, the ship is handed over to
a pirate crew (after properly screening them first, of course...). This means
that, for example, the Zhodani can raid Imperial shipping without using their
own warships and crews.
One little comment on pirates: traditionally, the pre-19th century pirates
would NOT kill a ship's crew, or even rob the individual crewmen, if the
crew surrendered without a fight. Many times, the pirates wouldn't even take
the ship, and even if they did, they made sure to land the crew on an island
with provisions. It should be noted that such merchant ships were owned by
companies, and thus the crews were just employees. However, many merchant
craft in Traveller are privately owned; either the pirates will have to go
in expecting a fight or will leave the independants alone. MY pirates (most
of them anyway) would rather not fight unless they have to, so will prefer
the company ships.