Many thanks for the ping. Nice bit of operational analysis here. Lord Percy saved the Brits from total disaster but it should never have proceeded - OPSEC was totally blown and a British officer learned about that in a tavern when a local drunk told him in some detail about the operation about to commence: "The Regulars will fail of their object." He was too late to tell Gage, however, whose wife Margaret was likely one of the intelligence sources - well, spies, to put it impolitely. Not that it was any real surprise anyway, because the Brits had telegraphed their punch with a previous maneuver.
The tactical objectives of seizing or destroying the armories came up far short due to the complete lack of operational security. They weren't (and Gage knew this) much of an excuse for starting a war even if successful; the actual objective was operational and it was to show the colonists that the troops were capable of such actions at will. That one came up catastrophically short - what it actually demonstrated was that they could be resisted.
Oh, and Samuel Whittemore. Anyone who doesn't know yet who he was is really missing out. ;-)