 The CSM for this flight , number 012 built by North American Aviation ( NAA ) , was a Block I version designed before the lunar orbit rendezvous landing strategy was chosen ; therefore it lacked capability of docking with the Lunar Module . This was incorporated into the Block II CSM design , along with lessons learned in Block I. Block II would be test @-@ flown with the LM when the latter was ready , and would be used on the Moon landing flights . 
