The superyacht Dilbar stretches one-and-a-half football fields in length. It has two helipads, berths for more than 130 people and a 25-meter (82-foot) swimming pool that itself can accommodate another superyacht.

Dilbar was launched in 2016 at a reported cost of more than $648 million. Five years later, its purported owner, the Kremlin-aligned Russian oligarch Alisher Usmanov, was already dissatisfied. He sent the vessel to a German shipyard last fall for a retrofit reportedly costing several hundred million dollars.

Dilbar was in drydock on Thursday when the United States and European Union announced economic sanctions against Usmanov – a metals magnate and early investor in Facebook – over his ties to Russian President Vladimir Putin and in retaliation for the Kremlin's invasion of Ukraine.

"We are joining with our European allies to find and seize your yachts, your luxury apartments, your private jets," President Joe Biden said during his State of the Union speech Tuesday night, addressing Russian oligarchs. "We are coming for your ill-begotten gains."

Seizing the behemoth boats could prove challenging. Russian billionaires have had decades to shield their money and assets in the West from governments that might try to tax or seize them.

Several media outlets reported last week that German authorities had impounded the Dilbar. But a spokesperson for Hamburg state’s economy ministry told The Associated Press (AP) no such action had yet been taken because it had been unable to establish ownership of the yacht.

Dilbar is flagged in the Cayman Islands and registered to a holding company in Malta, banking havens where the global ultra-rich often park their wealth.

Working with the U.K.-based yacht valuation firm VesselsValue, The AP compiled a list of 56 superyachts – generally defined as luxury vessels exceeding 24 meters (79 feet) in length – believed to be owned by a few dozen Kremlin-aligned oligarchs. The yachts have a combined market value estimated at more than $5.4 billion.

The AP then used two online services – VesselFinder and MarineTraffic – to plot the last known locations of the yachts as relayed by their onboard tracking beacons.

Many are anchored in the Mediterranean and Caribbean. But more than a dozen were underway or had already arrived in remote ports in small nations such as the Maldives and Montenegro, potentially beyond the reach of Western sanctions. Three had gone dark, their transponders last pinging just outside the Bosporus in Turkey – gateway to the Black Sea and the southern Russian ports of Sochi and Novorossiysk.

Graceful, a German-built Russian-flagged superyacht believed to belong to Putin, left a repair yard in Hamburg, Germany, on Feb. 7, two weeks before Russia invaded Ukraine. It is now moored in the Russian Baltic port of Kaliningrad, beyond the reach of Western sanctions imposed against him this past week.

French authorities seized the superyacht Amore Vero on Thursday in the Mediterranean resort town of La Ciotat. The boat is believed to belong to Igor Sechin, a Putin ally who runs Russian oil giant Rosneft, which has been on the U.S. sanctions list since Russia annexed Crimea in 2014.

The French Finance Ministry said in a statement that customs authorities boarded the 289-foot Amore Vero and discovered its crew was preparing for an urgent departure, even though planned repair work wasn’t finished.

The 213-foot Lady M was seized by Italian authorities Friday while moored in the Riveria port town of Imperia. In a tweet announcing the seizure, a spokesperson for Italian Prime Minister Mario Draghi said the yacht was the property of sanctioned steel baron Alexei Mordashov, listed as Russia’s wealthiest man with a fortune of about $30 billion.

But Mordashov’s the 464-foot Nord was safely at anchor on Friday in the Seychelles, a tropical island chain in the Indian Ocean not under the jurisdiction of U.S. or EU sanctions. Among the world’s biggest superyachts, Nord has a market value of $500 million.

"No self-respecting Russian oligarch would be without a superyacht," said William Browder, a U.S.-born and now London-based financier who worked in Moscow for years before becoming one of the Putin regime’s most vocal foreign critics.

Russian metals and petroleum magnate Roman Abramovich is believed to have bought or built at least seven of the world’s largest yachts, some of which he has since sold off to other oligarchs.

Dennis Cauiser, a superyacht analyst with VesselsFinder, said the escalating U.S. and EU sanctions on Putin-aligned oligarchs and Russian banks have sent a chill through the industry, with boatbuilders and staff worried they won’t be paid. It can cost upwards of $50 million a year to crew, fuel and maintain a superyacht.

Most of the Russians on the annual Forbes list of billionaires have not yet been sanctioned by the United States and its allies, and their superyachts are still crushing the world’s oceans. The 237-foot long Stella Maris, which was seen by an AP journalist docked this past week in Nice, France, is believed to be owned by Rashid Sardarov, a Russian billionaire oil and gas magnate.

The crash of the ruble and the tanking of Moscow stock market have depleted the fortunes of Russia’s elite. Cauiser said he expects some oligarch superyachts will soon quietly be listed by brokers at fire-sale prices.

On Thursday, the U.S. Treasury Department issued a new round of sanctions that included news release citing Usmanov’s close ties to Putin and photos of Dilbar and the oligarch’s private jet, a custom-built 209-foot Airbus A340-300 passenger liner.

"I believe that such a decision is unfair and the reasons employed to justify the sanctions are a set of false and defamatory allegations damaging my honor, dignity and business reputation," Usmanov said in a statement issued through the website of the International Fencing Federation, of which he has served as president since 2008.

Abramovich has not yet been sanctioned. Members of the British Parliament have criticized Prime Minister Boris Johnson for not going after Abramovich’s U.K.-based assets, which include the professional soccer club Chelsea. Under mounting pressure, the oligarch announced this past week he would sell the $2.5 billion team and give the net proceeds "for the benefit of all victims of the war in Ukraine."

Meanwhile, location transponders showed the 533-foot Solaris – launched by Abramovich in 2010 with an undersea bay that reportedly holds a mini-sub – was moored in Barcelona, Spain, on Saturday. Abramovich's $600 million Eclipse, eight stories tall and on the water since last year, set sail from St. Maarten late Thursday and is underway in the Caribbean Sea, destination undisclosed.