How would you organise your troops for a seige?

You can be UNSC, Covanent or Insurrectionists. This is a hypothetical scenario where you and your forces would initiate a seige on the ONI base from Halo 3: ODST, the one from New Mombasa. Example of layout below.

Faction: Which faction would you be?
Length of Siege: How long would you plan your Siege to be?
Vehicles,troops and ships used: Write a list of the troops, vehicles and ships you would use. You don’t have to go into to much detail.
Purpose of Siege: Write a quick explanation as to why you are attacking this base.
Layout of troops: How would you position your troops for an effective Siege?
Story: Again, you don’t have to go into much detail. Just a simple story of the events that will unfold during your Siege.
Tell me if there’s anything important I’ve missed, this is my first topic post. I just had a little idea and wanted to share it.

Well that whole level was already built around a siege and counter-siege scenario, but for the sake of discussion, I’ll just ignore the campaign’s story and set it up like this (oh and I chose to play as Covenant):

  • Background: After Regret’s departure, New Mombasa is in total mess. Covenant are pillaging the ruined city, and the UNSC is losing on every front. Insurrection underground terrorists were secretly plotting to seize control of the space elevator, but thanks to the recent breakout, their years of preparation are now meaningless, and they are now scattered across the city, struggling for their very own survival. After all, the Covenant don’t care about who’s who: humanity IS heresy! Also, the Creat Schism hasn’t yet happened in my case. - Battlefield: ONI Alpha Site. - Defensive: UNSC. They consist of regular ONI staff and security guards who just normally work there, ODSTs and Marines and civillian refugees. Due to how sudden the war started, they do not have serious defenses (just like how you don’t see heavy armor and anti-air missiles positioned around CIA in real life) aside from a few chaingun, gauss cannon and rocket Warthogs, most of which brought in by retreating troopers. ONI Alpha Site holds intel so critical that while it definitely cannot fall into the hands of the Covenant, it cannot be just destroyed either. All remaining UNSC forces are ordered to fall back to Alpha to buy its staff time to transfer the intel and then get evacuated by air and blow up the site. - Offensive: Covenant. They came to Earth with Forerunner sites in mind and found humans by coincidence. From years of war against humans they have learned of ONI and its roles. As ONI establishments possibly holds knowledge of their interest, they are heading towards Alpha aiming to steal Alpha’s intel. Like the UNSC, they can’t just simply bomb it. - Siege: My immediate problem is the restrained space on my side preventing me from stationing to many units at once and the fragile, narrow, long bridge that UNSC forces surely want to destroy. I will place one Wraith on each side of the bridge, sheltered behind stationary shields and keep lobbing plasma at UNSC’s end, blocking their access to the bridge but not harm the bridge itself. The shields are to maximize the Wraith’s survival rate against rockets and lasers, because if the tank gets destroyed, its debris will block my own reinforcements. If anybody sneaks through the Wraiths’ firing cycles, Jackal snipers will stop them. 4 Banshees will swoop around Alpha further distracting UNSC’s few heavy weapons, and take them out if whenever there’s a chance. 2 Spectres carrying Grunts and normal Jackals will force-land on UNSC’s both flanks to instill fear whether they success or not. After the heavy weapons are gone, shielded brutes will push across the bridge with a stealth Elite team behind them. the brutes will fight human infantry while the Elites rush inside the building. Jackal snipers then move in to secure the bridge. At the same time another Spectre(s) sends 2 more stealth Elite stealth teams and Shade turrets to Alpha’s roof. One team will intrude from the top while Shades and the other team will deny any potential UNSC airbound backup. As I successfully control Alpha’s exterior, broken UNSC and Insurrection squad start popping out behind my side. I don’t care about their intentions. Myy snipers and surviving Banshees and Spectres will hold them off. If that fail, then I’ll “retreat” to Alpha’s side and blow the bridge. I should have no trouble wiping out the remaining humans inside the building, then get the intel and finish.Only one point of failure: if humans already readied the explosives before my stealth Elites intruded, and determined the odds impossible, then they might just blow Alpha right away. And because transfering takes time, I will be on the defense the moment I conquer Alpha and need to watch out for airstrikes. Thus speed is of absolute essence.

Edit: I apparently messed up the names. I meant “Phantom” whenever I said “Spectre”.