The ISAR rebels were unaware of the IPF Deployment until the troops made contact near a Civic Square at the centre of the District, opposite its Local Government Complex. Rebel forces were expecting a limited deployment of Helian Planetary Defence Forces troops, acting on behalf of the Imperial Advisory, or at the least, armed Law Enforcement units from the HPDF, which further reduced their combat effectiveness as they realised they were engaging the ATIS Military directly.
However, the rebels managed to hold a defensive line near the Government complex, ironically using nearby housing facilities full of civilians to deter the Imperial forces from using heavy weapons. This plan ultimately worked, as the Directorship forbade collateral damage to prevent decay of the relatively pro-ATIS mindset of the everyday citizenship which had so far, prevented a major planet-side incident on Helia.
Despite this, the rebels failed to deter the Imperial troops, inflicting only minor losses and taking much greater losses themselves. Morale among the rebel forces was low, especially as the direness of their situation set in. Two armoured columns of the IPF Planetary Mechanised Infantry essentially boxed in the remaining rebels who had not surrendered outside the Local Government Complex within a few hours after the IPF touched down. Due to the high density civilian population nearby, the IPF commanders ordered the columns to hold position and draw the rebel fire away from the complex; while supporting Special Forces units were deployed via Spider gunships to the rear of the rebel position.
(Video) view from an IPF H-2045 'Prizrak' Infantry Fighting Vehicle as one of the armoured columns makes contact with the rebels defending the Civic Square.
The diversion strategy worked as the remaining rebel armoured units, consisting mainly of CEG-era T-270 MBTs and dismounted infantry engaged the IPF troops across the Civic Square, leaving the government complex with a lighter garrison - something the Special Forces units exploited to great effect. With their backs to the wall - the Civic Square being only a few hundred metres from the mighty Tier Division Block, the rebels believed their position to be defensible against ground assault but neglected to predict the IPF's use of low-flying troop transports to deploy small teams of special force units with greater flexibility, ultimately leading to the capture of the ISAR Rebellion leadership only six Helian planetary hours after the intervention began. With the leadership in Imperial Custody, the remaining rebels quickly surrendered or were neutralised by the IPF troops encircling the Civic Square.
With the 'head of the snake' removed, the seeds of dissidence quickly dispersed planet side, essentially securing the capital of the once great ISAR as a stronghold for the Aquarian Terran Imperial States in the Angel Reach. Despite the Imperial victory on Helia, elements of pro-independence forces scattered through the Helia system and outer sectors of the Angel Reach did remain, and sporadic skirmishes with Helia's newly established INSD contingent continued well into the 46th century. Despite this, the ATIS Directorship largely succeeded in bringing the once independent world firmly under the Imperial Flag without major bloodshed, and set a mostly positive outlook for the system going forward, with all the protection and economic benefits Imperial status afforded.