P-3s don't usually have radomes on top of them.
United States Customs Service P-3 AEW airborne early warning radar aircraft provide radar coverage wherever needed, including: the southern border, the Caribbean, or over international waters adjacent to as well as over source and transit countries. Established by Congress during the late 1960's in response to the growing number of airborne smugglers bringing drugs into the United States, the Customs Aviation Interdiction Program became operational in 1971. Its mission: to stem the flow of illicit drugs coming into the U.S. through the air and to assist other federal, state and local law enforcement agencies.
http://www.airliners.net/photo/US-Customs-&/Lockheed-P-3-AEW&C/1802345/M/