HereForTheBeer: Been a while since I played so I'm trying to remember details...

Are you having your tanks and anti-tank guns dig-in? This helps keep them alive longer. If you can, pull them back to get repaired before they are destroyed. You might also try flanking maneuvers if the attacks allow for it, since armor is weaker on the sides. Infantry can also destroy tanks with satchel charges (even if the squad has exhausted its anti-tank rounds). You'll likely lose most of the squad in the process but you only need one survivor to allow you to replenish the ranks using supply trucks.

For artillery, digging in helps. I don't count on aviation much but if you can make that work, then artillery is a good target for your planes. And use your own artillery for counter-battery fire.

HereForTheBeer: Crap - hotel internet ate my reply.

I don't know if it's a satchel charge or something else, and I don't think it shows up as part of the squad's ammo load. But get them to crawl close enough and they will try a very short-range bomb attack. You may have to change the squad's stance in order to get the guys to move in and attack instead of fleeing or seeking cover. And I usually had to click the target at least a few times to get them to attack.

Note that you can re-man the AT guns so long as the gun survives the encounter. And you can also capture enemy towed weapons in the same manner. Likewise, if at least one of the gun crew survives an attack, I believe you can use the supply truck to replenish the crew.

Blitz 1 and 2 handle squad resupply somewhat differently. This is outlined in another thread in this forum.

Personally, I found the Defend missions quite a bit more difficult. But they are also fun.