Following the attack on Pearl Harbour, forces destined for or already present in North Africa were diverted to the Far East to deal with the new threat. This stretched Commonwealth forces critically thin at a time when they were ready to exploit the victory won in Cyrenaica.
I have found the following list of units and formations transferred:
- 7th Armoured Brigade with two regiments.
- 1 Australian Corps HQ with: 6th and 7th Australian Division
- Transferred while in transit around the Cape: 18th (British) Infantry Division
I have not been able to find similarly detailed info yet. Those I have found:
- No. 211 Squadron (Blenheims)
- No. 11 Squadron (Blenheims)
- No.113 Squadron (Blenheim Fighters)
- Additionally a good number of single-engine fighter squadrons were transferred directly from the UK.
Gundelach, the German historian of the air war in the Med estimates that 300 planes were withdrawn from the theatre from December 41 to February 42. This is not including planes that were sent directly from the UK or the US to the Far East, instead of North Africa, so it understates the actual effect. To put this in context, the RAF started Crusader with about 750 planes.
(same proviso as RAF)
- HMS Abdiel (fast minelayer – she had laid the mines that sank 2. Panzerdivision in May 41)
- HMAS Hobart (cruiser)
- HMAS Yarra (sloop)
- HMAS Nestor, Napier, Nizam (all destroyers)
- HMS Truant (submarine)
- HMS Trusty (submarine)
- HrMs Isaac Sweers (Dutch destroyer), first to Netherlands East Indies, then to Eastern Fleet.
- Already transferred in November to accompany Prince of Wales and Repulse:
- HMS Encounter, Jupiter (destroyers)
This post on the AHF discusses the question.