The SUM-N-2 Grebe, also known as Kingfisher E and SUM-2, was a rocket- and pulsejet-powered anti-ship and anti-submarine missile developed by the United States Navy in the late 1940s.

Intended to allow a ship to deliver a torpedo at a significant distance from the launch location, it proved impractical in trials, and did not enter operational service.

[1] Kingfisher E, redesignated SUM-2 in September 1947 and SUM-N-2 Grebe in 1948, was a bulky yet conventionally-configured missile resembling a small unmanned aircraft, with a high-mounted, straight wing of 14 feet (4.3 m) span and a twin tail empennage configuration.

[2] Power was provided initially by a solid-propellant rocket, giving a range of 5,000 yards (2.8 mi; 4.6 km) at Mach 0.5; later in the design process a variant with a pulsejet sustainer engine was designed, weighing 3,000 pounds (1,400 kg) and boosting the missile's range to 40,000 yards (23 mi; 37 km) at a cruising speed of Mach 0.26.

[1] Although the concept of a torpedo-carrying pilotless aircraft failed to find favor with the U.S. Navy, the later French Malafon and Australian Ikara missiles are remarkably similar in concept and configuration;[4] the U.S. Navy would later develop the RUR-5 ASROC, a rocket-delivered torpedo (or a pure missile in the nuclear version), for attacking submarines at range.