A few moments later, the massive bulk of the Category A bulkhead's upper section began to move, retracting slowly upward as the rotary locking mechanism that secured both the upper and lower sections rotated ninety-degrees; locking bars withdrew into the mechanism one by one as the mechanism lifted up, following the metre-thick upper section upward. The lower section followed shortly after, lowering with a mechanical whirr and the sound of heavy actuators operating the one hundred ton bulkhead; which retracted neatly into the deck slot under the terminal inset by about ten centimetres. Retractable deck panels then extended over the gap to allow personnel and equipment to cross the threshold, locking into place with a series of metallic clicks. Once the opening sequence was completed, the amber 'standby' deck lights shifted to a green 'ready' status.
As the bulkhead opened, Dragon team had already begun surveying the other side for potential targets. Their helmet visors' advanced optics easily penetrating the clouds of vapour condensation created by atmospheric pressure normalisation. With their weapons firmly trained on the dozen-metre wide terminal, now firmly open, they awaited orders from Commander Kasake, who squinted slightly as he looked down the targeting optics of his weapon.
"Hold". He spoke quietly; but his voice was amplified over the personal helmet intercoms of the Marines' power armour. The Commander was waiting for the Imperial response; he had anticipated a full squad of the Imperial Navy's best Crimson counter-boarding troops to be laying in wait behind the bulkhead. In contrast, the much wider cargo-deck corridor leading to the access bay to the Central Elevator interchange was empty.
Kasake surveyed the scene with advanced optics; zooming in and analysing the corridor beyond the open bulkhead in variety of different wavelengths and active sensor patterns. Nothing. Not even the signs of an impromptu preparation for defence; things like up-turned crates forming makeshift barriers. Instead, everything was neatly in position as if no one had even expected the bulkhead to be opened, or there was simply no one present to respond.
Kasake knew something wasn't right, he knew the ship's crew would have been alerted to the bulkhead's opening, and they had already likely been tracking Dragon for some time on reserve internal systems. This must be a trap, he thought. Still, there wasn't time to sit and wait until something happened, Dragon had a job to do, and that job was to spring the trap and occupy the Imperial marines while the Captain infiltrated the command deck.
The Commander carefully gestured to the open bulkhead, updating the squad's battlesuit-net with new waypoints on the far side as the marines slowly advanced; their weapons trained on the opening with precision. Crossing the threshold, dragon split into two smaller teams as per the Commander's orders on the battlesuit-net, three marines went left in Alpha Team; taking up positions behind a loaded cargo mag-rail dolly which offered reasonable cover. The commander and the remaining two marines advanced right in Beta Team, hugging the far wall, making their way between storage crates on the side of the mag-rails, their weapons surveying every possible location that they anticipated a threat could arise from.
Kasake ordered Beta team to hold position as Alpha was in position; their weapons trained on the hundred metre or so portion of mag-rail transit way that linked the Category A bulkhead to the terminal to the elevator interchange; from there they could access the Reactor Complex directly. The commander kneeled behind a cargo crate; Beta team's two other marines on either side, covering his flanks. They were about two dozen metres ahead of Alpha team behind the stationary mag-rail cargo dolly; Kasake glanced back, nodding as he updated the battlesuit-net with new orders to hold and provide covering fire; Alpha was armed with the larger MX10M Assault Carbine which could be configured with a telescopic barrel assembly for precision, armour-piercing fire against armoured targets in larger open spaces such as this.
Complying, Alpha's marines switched to long-range firing mode; flipping a mechanical switch on the receiver of their MX10 rifles; the extendable barrel sliding into place along with a reinforced stock guard to counter the additional recoil. Targeting optics switched over to 4X variable as their helmet's Heads Up Displays changed modes accordingly. Each marine shouldered his rifle, gently placing the barrel over the top of the cargo dolly, all three business-ends facing towards the far terminal, ready to fire.
With Alpha in position, Commander Kasake considered his options. There was about another 100 or so metres of open deck, only a few sporadic, apparently discarded empty storage crates for cover leading up to the interchange bulkhead; another Category A, likely with a similar security system in place as the one prior. If the Imperials had garrisoned this passage - and the Commander considered that extremely likely - they would use this last stretch to spring their trap on Dragon team. Careful consideration was required as to how to approach the situation. Semper Marine Power Armour, based on enhanced TITAN-class Powered Exosuits developed for the Old Federal Marine Heavy Boarding Units was incredibly durable, but unlikely to protect the marines for long enough under fire from a directed Imperial marine squad emplaced on the far side of that Category A bulkhead. It was also unlikely that Dragon had enough time to approach the bulkhead's flanks before it fully opened, in which case Kasake considered they would have to withdraw back to the entry terminal, allowing the Imperial marines to gain the advantage.
(//continued in part b, need to take meds)