I have one question to the more knowledgeable of the Middle East theater: Why was the 4th Indian taken from the Western Desert to be sent to Sudan? It doesn't make sense to me.
In Sudan, the Sudan Defence Force had 3 British battalions and was reinforced by the 5th Indian division. In the South they had the 1st South African, 11th and 12th African divisions. It would be ASB to think that the Italians with what they had could capture Aden or even Port Sudan. If they advanced lets say 100 more miles in the interior of Sudan, it would not have matter at all. I understand that Massawa with its submarines and destroyers posed a bit of danger to the Read Sea life-line, but even so, its strategic value was far less that Tobruk or even Crete.
By sending the blooded 4th division (comprised by regulars and well-trained compared to other Indian formations during 1941-1943) and have a 2 week break of the advance, the chance was lost to actually fortify Cyrenaica and rest. In any case, I don't think it was plausible to capture Tripoli during Compass or in its afternath, even without sending the ANZACs to Greece. It all comes down to logistics. The distance to Tripoli is great and there is the possibility to suffer an even greater defeat than OTL in Sirte of Misurata instead of Cyrenaica.
Moreover, the British command failed to interdict the sea-lines after Taranto, fortify Crete and further reinforce Malta. There was a precious window of opportunity and it was not utilized. For example, only on the 21st of April the Mediterranean fleet bombarded (without much effect) Tripoli's port. Perhaps an earlier and more accurate bombardment would cause further delays in the arrival of the DAK. In Crete, the British after almost 6 months of presence, they had only to produce two hald-prepared landing strips and the placement of a handful of coastal guns. Lastly, to have a few Hudsons, Baltimores and another Stringbag squadron in Malta could have been a priority after Taranto instead of Q4 1941.
There was a chance to stand Rommel's attack in El Agheila or Benghazi. 2 or 3 extra weeks may have given some breathing space. I think it is quite possible to gain even a month of respite.
My stuff is naval and it is the Pacific, but from what I have learned so far, I can suggest the following.
1. There were a lot of armed Italians and colonial askaris in the AOI (Italian East Africa); about 300,000 of them. I think the Anglo-South Africans were outnumbered about 4-1 at least.
2. At least 1 veteran motorized formation who knew what they were doing would be necessary in the Sudan (north). The SA troopers were extremely good (south), but most of them were "amateurs" and they had to cross Ethiopia.
3. Sudan is on the way to Ethiopia, and the British were correct to be worried. Far too few troops and an extremely HOSTILE anti-British populace Note that the British had to put down several rebellions and they lost a whole army (Gordon 1885) in the Sudan less than 55 years earlier. It was also not certain the Italians could march up the Nile and make trouble.
4. Compass was an exploitation of a raid. Whether Tripoli was possible, I give it a 45% chance. Well worth the risk for the strategic dividends to be gained.
5. Surt as a fallback was possible to hold. Rommel at that stage was reckless and knew nothing about the desert. He could have been bagged as he was almost during Crusader and that op was just as bungled as anything O'Connor was likely to [not] screw up as Cunningham and Gort actually did during Crusader.
6.
the British command failed to interdict the sea-lines after Taranto, fortify Crete and further reinforce Malta.
(^^^) That warms the sea-power cockles of my heart. You know the RN was absolutely great at doing almost everything at what it did well and does, but those guys sure have major WW II issues and horrendous mistakes that British WW II historians gloss over. Technical stuff like air defense, aircraft carrier operations, early ASW and so forth is either misrepresented or distorted, but the thing that really hurts a factored balanced view of the RN is its failure to support the British desert army by being the sea guard, it should have been.
I also cringe when I see the accounts of the risks the USS Wasp ran in the Mediterranean to ferry planes and cover shipping to Malta, only to note the Spitfires she ferried are destroyed on the ground as they land at Malta or all those freighters get sunk. This not only happened with Wasp but many a British flattop risked her all and saw similar efforts go to naught because the Malta air and sea defense was not up to snuff.
One more reason to try for Tripoli. Or at least MINE the port!