The improvements normally take around four years to complete. The RCOH for USS "Theodore Roosevelt" took four years to complete (2009–2013) and cost about US$2.6 billion. Planned Incremental Availability is a similar procedure, although it is less substantial and does not involve refueling of the nuclear power plants. Because of their status as the largest warships in the U.S. Navy, the deployment of an aircraft carrier can fulfill a symbolic role, not just in terms of a deterrent to an enemy, but often as a diplomatic tool, in strengthening relations with allies and potential allies. The latter of these functions can take place either as a single visit to a country, in which senior naval officers are allowed to observe the operating of the carrier and to interact with its senior officers, or as part of an international task force. This can be in combat operations, such as NATO bombing of Yugoslavia in 1999, or other deployments involving training, such as Exercise RIMPAC. In addition, carriers have participated in international Maritime security operations, combating piracy in the Persian Gulf and off the coast of Somalia. As on most large warships, there have been several incidents involving the death or injury of one or more crew members, although most have involved freak accidents or failures, such as a man overboard as a result of poor weather. One of the highest-profile incidents was on 26 May 1981, when an EA-6B Prowler crashed on the flight deck of "Nimitz", killing 14 crewmen and injuring 45 others. Forensic testing of the personnel involved showed that several tested positive for marijuana. While this in itself was not found to have directly caused the crash, the findings of the investigation prompted the introduction of mandatory drug testing of all service personnel. In cases of ditched aircraft, pilots have been able to eject safely in several cases. However, fatal aircraft crashes have occurred; in 1994, Lieutenant Kara Hultgreen, the first female F-14 Tomcat pilot, was killed while attempting to land on board "Abraham Lincoln" during a training exercise. Fires have also caused damage to the ships; in May 2008, while rotating through to her new homeport at Yokosuka Naval Base in Yokosuka, Japan, "George Washington" suffered a serious fire which cost $70 million in repairs, injured 37 sailors and led to the ship undergoing three months of repairs at San Diego; this led to its having to miss the 2008 RIMPAC exercises and delayed the final withdrawal from service of . The fire was caused by unauthorized smoking in an area near improperly stored flammable refrigerant compressor oil.