On the edge of Tau space is the planet Lasat III. It has little value as a habitable planet, due to it being mostly mineral and having very little flora and forna. Its tactical value lays in the minerals within its crust.
Deep within the planet several veins of an exotic mineral often called Gellarthinite which is refined and used in the construction of warp drives for Imperial space ships. While not the only source of Gellarthinite in the galaxy, its loss would be a blow to interstellar vessel construction within the sector.
The Tau, ever an curious race, identified unusual energy readings from Lasat III and launched an exploration party to collect and research their discovery. The relatively small garrison present reacted and launched a pre-emptive strike on the Tau ships as they entered the system.
Their ferocious attack destroyed two interstellar ships and severely damaged a third forcing the Tau to withdraw, and call for reinforcements. However, what the Tau failed to realise was the garrisons assault had been a desperate distraction. Almost every available Imperial soldier in the capital of Lasat III had mobilised to repel the Tau and while they had succeeded, they had been wiped out virtually to a man. Only a few smaller garrisons in the outer lying townships had been unable to respond to the call to battle, leaving pitifully few soldiers left to defend Lasat III
An astropathic message went out for assistance. But the Imperium realised that they couldn’t afford to fight a protracted war over the Lasat system. It was simply too far from the nearest Imperial staging point and the impending threat of Hive Fleet Leviathan too great. So elements from two Space Marine Chapters set course for the beleaguered planet knowing they would have to inflict a mighty victory to force the Tau away from the planet forever.
The stage was now set for a battle of Apocalyptic Proportions!!
///data search/// planet designation: Lasat III....
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LASAT IIIMining World
Tithe Grade: secondus
Population: 100,000,000
Note: strategic ore production facilities

Lasat III is an unremarkable planet in the Lasat system. Bleak and inhospitable, its only value is in the mineral production facilities present. There are several veins of Gellarthinite present on the planet, which are important in the production of Imperial Warp engines.
Records indicate that there are two major urban areas. Lasat Primus and Lasat Secundus. When the colony was originally founded it was built on the site of what is currently Lasat Secundus, with mining facilities to the north. However, a greater vein of mineral Gellarthinite was found and a new facility constructed adjacent to it. This vein produce more regular yields than the mine at the original colony and eventually a new conurbation developed around it.
Following the move of the Governor and the political hub the new city was named Lasat Primus and the original city renamed Lasat Secundus.
LASAT PRIMUS
The administative hub of Lasat III as well as the main industrial heart.
Gellarthinite ore gathered from the deep surface mines is processed and transported directly to the main start port to the north.
Lasat Primus itself is constructed to the east of the mine workings.
Main PDF garrisons located near Spaceport with command hubs located at the spaceport and Central Command located near the Govenors palace.
Est. Population: 60,000,000
LASAT SECONDUS
Site of the original Lasat colony. City in industrial decline due to iregular output of Gellarthinite ore. Industrial and administative management relocated to Lasat Primus in late M37.
Small starport maintained for extraction of ore as and when its processed.
Small subsiduary garrison. Situated to protected the Starport. Minor command hub located on garrison.
Est. Population: 20,000,000
/// Inquisitorial Records indicate that Inquisitor Tirpiz examined the population at some point in M38,400 and found popular dissatisfaction with the administrative move in members of Lasat Secundus. However while the population was generally unhappy with the redesignation there were no signs of open or covert rebellion. ///