Minisphere Pirates
It is 2218, a decade after the Treaty of Sirius brought an end to the Zodiac War. This war had, at one point or another, engulfed most of the Pacific Arm. A staggering array of weapons were deployed and stratagems ranging from the latest infoattack methods to techniques old when the first spaceships lumbered out of Earth's atmosphere. Among the latter was the issuance of Letters of Marque by several Zodiac states, allowing for armed auxiliaries to fight for their nation. After the war some gave up their letters or had them revoked. Others kept their status as privateers.
This is their story.
Privateering in the 23rd century
Human space is a dangerous place. Most of this danger comes from Velan mechanolife, sometimes-aggressive self-replicating machinery that is the remnants of an alien civilization otherwise dead for millions of years. Awoken by humanity's bumbling exploration they have once again started on their ancient, enigmatic tasks. While warships of various nations keep these semisentient machines away from busy shipping lanes and inhabited worlds, anyone going outside of tightly-patrolled space is advised to carry a weapon - just in case. This has bred a certain rugged self-reliance among those who travel the spaceways and it is from these that modern-day privateers are drawn.
The first official privateers of this new stellar age were called up in the Shore War of the late 2180s by the young Zodiac organization. They accepted a commission to put their civilian ships - often idled since the Breakdown of 2172 - into paramilitary service, receiving arms, refits and precious repaired FTL jump drives. Many of these were patriotic Hampshirans though eventually privateers hailed from all Zodiac worlds, filling in during the first phase of the war until purpose-built warships were built in sufficient numbers to replace them. A strong minority eventually joined the military organizations but most retained their autonomy, fighting alongside but not under the 'official' militaries.
(Note that this differs from the Solomonic War where both sides rapidly nationalized every ship capable of carrying a gun or missile - by the end of the Solomonic War the 'private' interstellar spacecraft had all but disappeared and only reappeared in the post-war drawdown of forces.)
These civilian conversions were sometimes ramshackle, often inefficient and never identical, but the valor of those who served onboard was rarely found wanting. They would go on to fight in all major and most minor engagements of the war and by the endgame around Heaven's Shore and APEX-579 their status has been legally formalized. Still independent, but with the full force of Admirality law behind them.
Many privateers maintained their commission in reserve even after hostilities were completed and their ships were returned to (mostly) unarmed civilian configurations. A few carried on, becoming xenomachinery hunters operating on the fringes of Zodiac space and into the now-reopening PACT and Euro arms. All this would have been a historical curiosity and a colonial expedient if not for the descent into hostilities between several members of the Zodiac organization and their original national sponsors in the early 2200s - this was to become the Zodiac War.
Many privateers rushed to reactivate their commissions and rearm their ships, throwing themselves into the war once again. The enemy this time was not Shivans and exhuman reavers using ships and weapons not particularly different from those of the privateers themselves though, but the dangerously well-equipped and highly organized militaries of the Core. After the first few embarrassing and disheartening losses these auxiliary crews and ships shifted their targets to softer ones - civilian shipping and unprotected bases.