The assault team went in in two specialist helicopters with low noise and very small radar signatures. They flew into a city that had just been blacked out and they weren’t flying in blind; the ground team that provided the black-out were also there to provide intelligence on the situation on the ground, had there been any army activity in the city the assault would not have preceded. So interception of the team before they reached Bin Laden’s compound can be largely ruled out.
Abbottabad is a quiet city in the north of Pakistan, well clear of the Afghan border and not prone to disturbances, no doubt this is why Bin Laden chose it to hide in. Although there is an army garrison in the town it is unlikely that they were in any kind of state of alert, in all likelihood they had a platoon on standby as ready reaction and a company designated as on duty to back them up. Since the attack took place in the early hours of the morning the ready reaction platoon was in the common room watching a movie or playing cards, and cursing the lights having suddenly gone out, or dozing on bunks next door. The first anyone at the base would have known anything was amiss would be at the sound of the Blackhawk crashing in Bin Laden’s compound, if they were even close enough to hear it.
So the first the Pakistani authorities know anything is happening is when they hear a crash or someone telephones it in to them. Initial thoughts would be that the crash has somehow caused the blackout or been caused by the blackout. Either way the first response is going to be fire brigade or ambulance rather than military, it is only once the shooting starts in the compound that that is likely to change.
Assuming the duty officer at the barracks responds promptly to initial reports and immediately stands too the ready reaction force they aren’t going to spring instantly into action; this is occurring late at night (after midnight) and the city is now blacked out; men are stumbling around just trying to find torches with which to locate the rest of their kit with. By the time all members of the ready reaction force is awake, kitted out and sitting in land rovers and trucks you’d be lucky in less than fifteen minutes has gone by, it’d be miraculous if anyone’s rolling out the front gate in less than half an hour.
So the Pakistani ready reaction force, in three or four vehicles rolls out the front gate in the direction of gunfire and explosions. They still have no idea what is going on. At the first sign of significant activity in the barracks the American back-up force, in three Chinook helicopters, would move in from where they’d been loitering outside the city and move to intercept the vehicles well before they got close to the target compound. The Pakistani’s would find themselves coming under fire from the air. The shooting would be precise and coming from multiple directions. This is not a situation that would appeal to many and would promptly halt the vehicle convoy.
The Pakistanis would then be pinned down until the assault team had completed their task and been extracted, at which time the backup force would break off their action and depart.
At which point the diplomatic shitstorm would begin.