The Malaysian Air Force is converting two of its CN-235 twin-turboprop transports into maritime patrol aircraft. This involves equipping the transports with the Merlin maritime surveillance system provided by an American firm. This system is similar to the one being used in U.S. Coast Guard CN-235 transports. That one uses military-grade naval search radars. The Merlin system is already operating on three CN-235s used by the Indonesian military so the Malaysians had an opportunity to see how that worked for their neighbor and know what they are getting.
The U.S. Coast Guard has 18 HC-144 ("Ocean Sentry") MPA (Maritime Patrol Aircraft) that are basically CN-235s converted to maritime patrol aircraft. The coast guard wanted 36 of these aircraft but budget problems halted acquisition at 18. The first one entered service in 2006 and carried out its first search and rescue mission in 2008. By 2011 HC-144s had flown 10,250 hours on patrol missions. Some were over land when there was a natural disaster that needed air recon quickly.
The Ocean Sentry is actually a militarized CN-235, which is a cheaper ($19 million each) alternative to the larger, four-engine P-3 and P-8 aircraft the U.S. Navy uses for high seas recon. The CN-235 suits the coastal patrol needs of the coast guard in just about any nation.
The CN-235 is a civilian twin-engine, 15-ton aircraft with a max payload of six tons. With about three tons of sensors and other equipment, a typical load for an MPA, the CN-235 can stay in the air for up to eleven hours per sortie. Most missions are about ten hours. Cruising speed is about 435 kilometers an hour. The CN-235 is equipped with a thermal imager and electronic monitoring equipment, in addition to the sea search radar. Malaysia and Indonesia will use their CN-235 MPA to keep watch for smugglers, Islamic terrorists and foreign fishing boats illegally fishing. The Chinese are the most brazen poachers and Indonesia is one of their favorite poaching grounds. Recently several dozen Chinese fishing boats, accompanied by armed Chinese coast guard ships arrived off Indonesia to steal a lot of fish. The Chinese have done this before and will only heave if a more heavily armed Indonesian ship shows up and fires a few warning shots. Malaysia and Indonesia both have problems with China claiming some of their offshore water rights. This is part of the Chinese effort to take control of most of the South China Sea, including all the economic treasures found there (fish, natural gas, oil and so on.)
Several nations have adapted twin-engine business jets as maritime patrol aircraft. This is a more expensive option but provides a faster aircraft that can patrol offshore areas faster or simply get to a patrol area faster.