The Roles and Weapons with the Squad

[JMA]

...and what standard defensive principle would those be?

A FOB is a facility from which to mount operations, and the location itself may provide operational advantages, such as surveillance of a route or an area. The Surveillance Towers in South Armagh, were sited to give the most efficient coverage of the boarder. Had a Soviet MRR been coming north from the Republic, they would not have been where they were.

A FOB in A'Stan is in a very, very low threat environment. Siting is in no way critical. Taking on a proficient mobile enemy with AFVs is a different game altogether.

Having said that, the base at Wanat was clearly badly sited and there for all the wrong reasons. The SF Base at Lang-Vei, over run during Tet, was never constructed with Tanks (PT-76's) in mind. Compare and contrast, the SF Base at Kontum, which straddled the main road.

The differentiation is really all down to your core functions analysis. A FOB in A'Stan is "Found." If you were an Armoured Coy in Germany facing the Soviets, and you got "found" you were probably going to be dead before the fight began.

May I suggest that you access and read the following without delay:

Army Field Manual (AFM)
Volume One - Combined Arms Operations
Part 10 - Counter Insurgency Operations
ANNEX B TO CHAPTER 8
FORWARD OPERATIONAL BASES

All will be revealed.

OK so getting found is the problem. So in the defence you have have resources that will find the enemy forming up/gathering/grouping then you have the ability to break up their attack before it begins, yes?
(See:
ARMY FIELD MANUAL
VOLUME 1 COMBINED ARMS OPERATION
PART 1 - FORMATION TACTIC
PART 2 – THE CONDUCT OF FORMATION LEVEL OPERATIONS
SECTION 4 — OFFENSIVE SUPPORT
712. General
a. (1) Engaging the enemy early to disrupt the cohesion of his attack, reduce his information gathering capability and his ability to mass combat power.)

OK, so that said you also need to make urgent reference to the following:

ARMY FIELD MANUAL
VOLUME 1 - COMBINED ARMS OPERATION
PART 2 - BATTLEGROUP TACTICS
PART B - TACTICS AT THE BATTLEGROUP LEVEL
CHAPTER 7 - DEFENSIVE OPERATIONS
SECTION 1 - THE FUNDAMENTALS

Trust me its all there...

The problem in Afghanistan is that "young" and inexperienced Brigadiers, Lt Cols and majors have been allowed to make it up as they go along.

...sadly the Brits have never been able to learn from their own mistakes. I'm told by those who know that it is due to the levels of arrogance which rise in step with officer promotions. That is why it is widely accepted that apart from a rare few, British officers are mainly followed out of curiosity.