Cymrudia

Cymrudia is an ocean planet located in the Mellt Cluster in Segmentum Ultima. Although on the Imperium - Tau border the planet wasn't overly desired by either due to the limited amount of land on its surface. As the Imperium claimed more and more worlds in the frontier Cymrudia was settled to provide fish, plankton, and desalinated water to the surrounding planets.

The world's oceans dominated the planet, however several small islands broke the surface. As more and more water was taken off planet these islands grew larger, resulting in a growing population. Eventually Cymrudia had a large enough stable population that it was required to pay it's tithe to the Imperium in the form of regiments for the Astra Militarum. Since then a single regiment has been raised every planetary year, taking men and women from each of the 5 main islands and combining them into a Cymrudian regiment. The islands are named Ulreth, Bedr, Giliarth, Valdeer, and Krip. Each of the islands have their own distinct set of traditions and cultures. Initially this resulted in some mixed results when combining the people from the various islands into the combined regiments. With such proximity to Tau and various other Xenos races xenophobia is encouraged in the frontier worlds. Generally following the formation of a regiment the soldiers all bonded together well after a stint of mistrust, knowing that they would be battling xenos soon enough, and that they were part of something greater. This ingrained mistrust of outsiders was the root of the downfall for the Cymrudian 3rd however.

After almost two centuries of falling sea levels the mineral wealth hidden beneath the ancient oceans became easily exploitable. A small portion of the profits made from trading these riches were used to help equip the Cymrudian regiments with a variety of vehicles which would be impossible to produce on Cymrudia. With Imperial forces withdrawing from the cluster to fight against hive fleet Leviathan, the T'au considered it valuable enough to risk the wrath of the Imperium and to take the planet by force.  The T'au launched a full scale assault to capture the planet so as to use the mineral wealth there to bolster their own armies in order to aid the launch of another sphere of expansion. They had planned to arrive after the newest regiment had been taken off world, but the imperial troop transport ship arrived 2 months later than planned after exiting the warp. The newly formed Cymrudian 209th were in the process of boarding when the T'au invasion started. They tried to hold off the invasion but were inexperienced, outnumbered, and outclassed. After a short bloody battle the order to retreat was given and the 209th made a brake for their transports to get off world to the warp where the T'au wouldn't follow.

Cymrudia is now firmly in T'au control and the T'au are pushing on to other imperial planet's in the  cluster. Many humans on these captured worlds have joined the greater good and now fight alongside their invaders as Gue'vesa. These traitors are held in upmost contempt by the men and women of the 209th.

The 209th are now under the command of Lord General Thaedus Quinn, who has been tasked with bringing back the light and strength of the Imperium to the frontier.