Battle units not being used

Can't understand this either. The M2-Light Tank has a defense of 60 same as the Thor. If that is the case, why are my M2 not being used? They should be right under the Thor, but not even listed.
1 x Libyan Rebel Truck (63 Defense)
1 x British MBT (62 Defense)
448 x Thor (26880 Defense)
34 x Armored Bulldozer (2040 Defense)
5 x Fuel Tanker (300 Defense)
1 x Desert Tiger (56 Defense)
7 x IMZ Ural M-72 (385 Defense)
6 x AT-Goliath (330 Defense)
77 x M7-A7 (4081 Defense)
5 x M1078 Truck (265 Defense)
26 x Chinese Ground-to-air Vehicle (1378 Defense)
1 x Haunted Tank (52 Defense)
45 x Truck Convoy (2340 Defense)
5 x MPUV Loader (250 Defense)
9 x Asian Armored Vehicle (450 Defense)
25 x Soviet T34 (1250 Defense)
5 x M35 Truck (250 Defense)
979 x T-1 (47971 Defense)
5 x Cargo Supply Truck (235 Defense)
56 x Missile Launcher Vehicle (2576 Defense)
1 x Anti-aircraft Truck (45 Defense)

nevermind, once again I can't use until level 520. figured it out