The Bluefin-21 is an autonomous underwater vehicle (AUV) developed by Bluefin Robotics for defence, commercial or scientific use.
 It found its most famous use in April 2014 in the search for the wreckage of the missing Malaysia Airlines Flight 370.
The Seaglider is a deep-diving Autonomous Underwater Vehicle (AUV) designed for missions lasting many months and covering thousands of miles.
 In military applications the Seaglider is more commonly referred to as an Unmanned Underwater Vehicle (UUV).
The Deep Phreatic Thermal Explorer (DEPTHX) is an autonomous underwater vehicle designed and built by Stone Aerospace, an aerospace engineering firm based in Austin, Texas.
 It was designed to autonomously explore and map underwater sinkholes in northern Mexico, as well as collect water and wall core samples.
 The DEPTHX vehicle was the first of three vehicles to be built by Stone Aerospace which were funded by NASA with the goal of developing technology that can explore the oceans of Jupiter's moon Europa to look for extraterrestrial life.
Petrel (Hai-Yan or Haiyan, 海燕) hybrid underwater glider (HUG) is a Chinese autonomous underwater vehicle (AUV)/Autonomous underwater glider (AUG)/Remotely operated underwater vehicle (ROUV) developed by Tianjin University.
 After the initial Petrel, a follow-on Petrel II has also been fielded by the same developer.
RU-27, dubbed Scarlet Knight after the Rutgers Scarlet Knights athletic teams, is an experimental American autonomous underwater vehicle – a modified Slocum Autonomous Underwater Gliding Vehicle – operated by Rutgers University oceanographers.
 In December 2009, "Scarlet Knight" was the first robot to cross the Atlantic Ocean underwater, which took it 221 days.
Malaysia Airlines Flight 370 (MH370/MAS370), registered as 9M-MRO, was a scheduled international passenger flight that disappeared on 8 March 2014 while flying from Kuala Lumpur International Airport, Malaysia, to its destination, Beijing Capital International Airport in China.
 The aircraft, a Boeing 777-200ER operated by Malaysia Airlines, last made voice contact with air traffic control at 01:19 MYT, 8 March (17:19 UTC, 7 March) when it was over the South China Sea, less than an hour after takeoff.
 The aircraft disappeared from air traffic controllers' radar screens at 01:22 MYT.
 However, Flight 370 was still tracked on military radar as it deviated westwards from its planned flight path and crossed the Malay Peninsula.
 It left the range of Malaysian military radar at 02:22 while over the Andaman Sea, 200 nmi north-west of Penang in north-western Malaysia.
 The aircraft was carrying 12 Malaysian crew members and 227 passengers from 15 nations.
An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring input from an operator.
 AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification that includes non-autonomous remotely operated underwater vehicles (ROVs) – controlled and powered from the surface by an operator/pilot via an umbilical or using remote control.
 In military applications a AUV is more often referred to as unmanned undersea vehicle (UUV).
 Underwater gliders are a subclass of AUVs.
SPURV, or Self-Propelled Underwater Research Vehicle, was an Autonomous Underwater Vehicle built in 1957 at the University of Washington's Applied Physics Laboratory.
 The research and development of this vehicle was funded by the United States Office of Naval Research (ONR), and it became the US Navy’s first autonomous underwater vehicle (AOV).
 The navy used a total of 7 SPURV vehicles until 1979.
AUV (Autonomous Underwater Vehicle) - 150 is an unmanned underwater vehicle (UUV) being developed by Central Mechanical Engineering Research Institute (CMERI) scientists in Durgapur in the Indian state of West Bengal.
 The project is sponsored by the Ministry of Earth Sciences and has technical assistance from IIT-Kharagpur.
Nereus was a hybrid unmanned autonomous underwater vehicle (HROV, a type of remotely operated underwater vehicle) built by the Woods Hole Oceanographic Institution (WHOI).
 Constructed as a research vehicle to operate at depths of up to 11000 m , it was designed to explore Challenger Deep, the deepest surveyed point in the global ocean.
 "Nereus", named for Greek sea titan Nereus (who has a man's torso and a fish-tail) through a nationwide contest of high school and college students, began its deep sea voyage to Challenger Deep in May 2009 and reached the bottom on May 31, 2009.

Question: Which Malaysia Airlines disappeared in 2014 that required an autonomous underwater vehicle Bluefin-21 to help look for it?
Answer: Malaysia Airlines Flight 370