The senior-most US military commander in the Middle East, US Central Command chief Admiral Brad Cooper, visited the USS Abraham Lincoln in the Arabian Sea on Saturday (August 15), amid claims of food shortages, flagging morale, and even suicide attempts on the aircraft carrier. The USS Abraham Lincoln has been at sea without a break for over 260 days.While US President Donald Trump has dismissed reports of hardships on the USS Lincoln, the USS George Washington is leaving the Pacific Ocean, at a time China has been assertive about its territorial claims in the region, in all likelihood to replace the long-deployed carrier in the Arabian Sea.What has gone wrong aboard the USS Lincoln? What exactly are aircraft carriers, and what does this episode say about their continued relevance? We explain.What is an aircraft carrier?An aircraft carrier is basically a mobile airbase.A land-based fighter plane can fly hundreds or even thousands of kilometres out over the ocean. But after it completes its mission, it needs somewhere to land. It also needs fuel, weapons, maintenance and people to service it. A carrier takes all of this with it.A carrier can launch fighter jets to attack targets, intercept enemy aircraft and defend the fleet. Other aircraft and helicopters can search for submarines. Specialised aircraft can provide early warning, essentially acting as flying radar stations. The carrier can therefore serve as an airbase miles away from a country’s territory.What is happening aboard the USS Abraham Lincoln?The USS Lincoln has been at sea for over eight months now, three months behind its original target of May. It has been parked in hostile territory, amid a naval blockade of the Strait of Hormuz by both Iran and the US, so vessels carrying mails and fresh rations have faced difficulty reaching the carrier and the 5,000 personnel abroad.Story continues below this adAlso in Explained | Hamas has agreed to disarm. So why is Israel still refusing to leave Gaza?For more than a month now, there have been reports of deteriorating conditions aboard the ship. At a town hall with senior US Navy officers held earlier in August, families spoke of sailors feeling distressed, and at least two trying to jump overboard.The claims have now gained political mileage. Democrat Congressman Mike Levin, who serves on the Veterans Affairs committee, posted on X on August 11, “It’s been a week since a dozen military families shared what their loved ones are enduring aboard the USS Abraham Lincoln. Moldy showers, broken toilets, laundry down for weeks, long stretches with no hot water, a meal that came down to half a cup of rice and two tortillas. No soap, deodorant, or toothpaste.”Trump and Secretary of War Pete Hegseth have downplayed the reports.On August 15, Acting Secretary of the Navy, Hung Cao, said as part of a longer statement, “A small number of mental health cases were treated with no loss of life. Meal plans were adjusted when fresh resupply was unavailable, without a single meal being missed. Calls home were limited when the operational threat was too high. There is no question our young men and women have been pushed to their limits—but they have never broken. They are rightly tired—but have never been out of the fight.”So why are aircraft carriers so important?Story continues below this adThe US kept the USS Lincoln deployed well beyond the initial target, and is now moving away a ship from China’s vicinity to replace it, showing the centrality of aircraft carriers to its war strategy. Yet, the importance of carriers has often been questioned.An aircraft carrier is a huge, hulking, visible target — the USS Lincoln is around as tall as a 20-storey building. Some experts argue that in the age of missiles, drones and submarines, should countries still spend billions of dollars on building, deploying, and maintaining aircraft carriers?After all, if an enemy could successfully sink one, the loss would be enormous — militarily, financially and politically.Also Read | What the entry of the Houthis means for the US-Iran conflictHowever, aircraft carriers are also very good at dodging as well as absorbing damage. A US carrier normally operates as the centre of a carrier strike group. Around it are destroyers and other warships equipped with radar and air-defence missiles, as well as submarines and supply ships. Aircraft operating from the carrier provide another layer of protection.Story continues below this adAn enemy does not merely have to fire a missile at a carrier. It has to get a weapon close enough, penetrate the carrier group’s defences and hit a moving target. And even being hit does not necessarily mean the carrier is destroyed.Aircraft carriers have specialised teams trained to fight fires, contain flooding, repair damaged systems and keep the ship functioning after an accident or attack. Sailors regularly practise responding to fires, burst pipes, flooding and other emergencies.The US Navy has learned some of these lessons the hard way. In 1967, a fire aboard the USS Forrestal killed 134 people, injured 161 and destroyed 21 aircraft. The disaster led to major changes in firefighting, damage control and the handling of ammunition aboard carriers.Story continues below this adDoes India have aircraft carriers?Yes. India currently operates two aircraft carriers — INS Vikramaditya, the refurbished former Soviet-era Admiral Gorshkov, and the indigenously built INS Vikrant. The Navy has also sought a third carrier to expand its ability to maintain a sustained presence in distant waters.VIKRANT:INS Vikrant was the first indigenously built aircraft carrier of the Indian Navy. With a displacement of 45,000 tonnes, it is the largest warship ever built in India. The Navy says roughly 76% of the carrier comprises indigenous content, including 23,000 tonnes of steel, 2,500 km of electric cables and 150 km of pipes.Expert Explains | Indian Navy’s long and illustrious road to an Indigenous Aircraft CarrierVikrant can carry up to 34 aircraft, with Russian-made MiG-29K fighter jets as its primary combat aircraft. It has a crew of about 1,600 and functions almost like a small town at sea, with a hospital featuring two operation theatres and an ICU, workshops, and three galleys.VIKRAMADITYA:INS Vikramaditya, commissioned in 2013, was originally the Soviet-era Admiral Gorshkov, which India acquired from Russia and had refurbished. It operates MiG-29K fighter jets using a ski-jump for take-off and arrester wires for landing.VIRAAT:Story continues below this adBefore Vikramaditya and Vikrant, India operated INS Viraat, formerly the British HMS Hermes. Commissioned by the Indian Navy in 1987, Viraat participated in Operation Pawan, the Indian Peace Keeping Force mission in Sri Lanka, and later in Operation Parakram in the North Arabian Sea. It was decommissioned in 2017.