Although Boulogne has fallen and Calais appears to be considered indefensible as part of the evacuation perimeter, with the extra days provided by the successes at Arras and around Calais, would it be possible to hold the Dunkirk perimeter such that the Eastern and Western Moles can be maintained for evacuation? This would have a massive impact on the ability of larger ships to load men and equipment. This relies on the potential of the moles being recognised before the bulk of the troops are located on the Eastern beaches.
There's worked up infantry tanks in Calais, and this time they're on the defensive. 'Indefensible' is a matter of opinion, at least for a time.
Problem with the Moles is they are a prime target for the LW and artillery
With Calais still in Allied hands, the ships can use Route Z, which means the air-defense perimeter is much shorter, so the LW will have fewer chances to bomb them anyway.
But there's the issue of having to defend more space, and whilst we know now that artillery or the Luftwaffe was unable to destroy the East Mole, they didn't at the time and it was more a case of "All its going to take is one well placed bomb or shell."
Calais is far more defensible here. OTL tanks in Calais belonged to 3rd RTR, which had 21 light tanks and 27 cruisers. Here it's 8th RTR that's there, and they're equipped with Light tanks and
Infantry tanks (mixed A11 and A12). It'll make Calais a tough nut to crack.
Germans were pretty effective in making all the Channel ports unusable through mass bombing raids - at least for the duration of the evacuation. You'd need a much better performance by the RAF to keep any of the ports open for longer than a day or two more.
The RAF have a markedly narrower perimeter to maintain here, so the LW won't have as easy a time penetrating.
Wow, some of you guys are really hung up on evacuating out of Calais. Sure, it's a possibility but I wouldn't call it that likely. Just a few more days out of Dunkirk will make all the difference in the world compared to OTL, regardless of if the BEF has a second port to load from.
It's not evacuating from Calais that's the big question it's holding it. Holding Calais means the ships to Dunkirk can use the much shorter Route Z, which will save a nor insignificant amount of time, and is a significantly shorter perimeter for the RAF to defend, making it harder for the LW to penetrate. It not only means a faster, more comprehensive evacuation, it also means fewer ships destroyed or damaged.