Claymores can only be equipped by playing as the Engineer class (cog symbol.) This can be boosted with a friend in a private Free For All or Team Deathmatch. Alternatively, you can easily achieve this in Initiation B (Afghanistan) co-op mission. Once you exit the chopper, select your claymore by pressing twice and start sprinting forward and up the stairs where several enemies will spawn from (around 6-8.) At this point simply place your claymore in the middle of that room and run away so you’re not killed in the blast. Seconds later you should get 3-6 kills depending on how many enemies were close to the blast. Repeat until you reach 30 kills.