Boeing is building seven B-737 aircraft modified to serve as the U.S. Navys replacement for the P-3 maritime reconnaissance aircraft. These seven MMA (Multi-mission Maritime Aircraft) will be used for testing and development before mass production of over a hundred MMAs begins before the end of the decade. 

Although the B-737 MMA is a two engine jet, compared to the four engine turboprop P-3, it is a more capable plane. The MMA has 23 percent more floor space than the P-3, and is larger (118 foot wingspan, versus 100 foot) and heavier (83 tons versus 61). Most other characteristics are the same. Both can stay in the air about ten hours per sortie. Speed is different. Cruise speed for the MMA is 910 kilometers an hour, versus 590 for the P-3. This makes it possible for the MMA to get to a patrol area faster, which is a major advantage when chasing down subs spotted by sonar arrays or satellites. However, the P-3 can carry more weapons (9 tons, versus 5.6.) This is less of a factor as the weapons (torpedoes, missiles, mines, sonobouys) are, pound for pound, more effective today and continuing that trend. Both carry the same size crew, of 10-11 pilots and equipment operators. Both aircraft carry search radar and various other sensors. The 737 has, like the P-3. been equipped with bomb hard points on the wings for torpedoes or missiles.

The B-737 is a more modern design, and has been used successfully since the 1960s by commercial aviation. Navy aviators are confident that it will be as reliable as the P-3 (which was based on the Electra civilian airliner that first flew in 1954, although  only 170 were built, plus 600 P-3s. About 40 Electras are still in service). The Boeing 737 first flew in 1965, and over 5,000 have been built. The MMA will be the first 737 designed with a bomb bay and four wing racks for weapons.