How do I get a nuke on MW2?

the only nuke i got was playing on HC domination. using the m-21 sniper. my kill streak was the apache, ac 130 and nuke stayed far away and sniped people. killcam doesnt show so when people realized the area i was shooting at, i just moved around the same area after 3-5 kills so they cant find. and when ther look for me i kill them