Operation Crossroads (1946) was two atomic bomb tests where the second one was exploded under water creating a radioactive steam cloud that spread over all of the ships, including the support ships thus irradiating about 80% of the US Pacific Fleet at the time. The Navy had set up a set of Target Ships including the Saratoga and Independence Aircraft Carriers to see what effect a nuclear explosion would have on the ships. The explosion irradiated the water in the lagoon the equivalent of 5000 tons of radium.

Unfortunately they miscalculated and thus irradiated all of the ships present which had to be cleaned immediately to be put back in action. Thus the ships had to go to US Ports and be cleaned by sandblasting and the Navy decided to dump the contaminated sandblast sands directly into the harbors of the Navy Bases. 145 out of 207 ships were sent to be decontaminated, the others were scuttled. Airplanes were sent to their respective bases to be washed down.

The Navy entered the Lagoon with the support ships but had to retreat when the radiation levels exceeded the fatal level and the ships ran out, some went out to sea to escape. One hour after the blast the Battleship “New York” had a reading of 1200 r/hr which is 3 times the fatal dose. Here is a video of the scene, showing the support ships wash down the decks of the target ships like it was a carwash, the sailors completely unaware of the danger of a nuclear blast. https://youtu.be/BKH437o14vA

145 out of 207 ships were sent to be decontaminated, the others were scuttled. There were also airplanes that were affected and they had to return to their bases to be decontaminated. The ships were sent to the following ports to be cleaned:

• Bremerton and Puget Sound
• Guam/Marianas
• Hunters Point Shipyard – San Francisco
• Kwajalein
• Mare Island
• New Orleans
• Norfolk
• Los Angeles
• Pearl Harbor
• San Diego
• San Pedro
• Terminal Island
• The Caroline Islands
• The Philippines
• Treasure Island – San Francisco

The ships had to be sandblasted to remove the paint in order to clean the ships. Because the non target ships used their pumps and hoses to clean the other ships or operated inside the lagoon, their water lines, pumps and evaporators (used to produce clean water) were contaminated and in most cases they could clean them with acid which was also dumped directly into these harbors. At the time the Navy was only concerned with the effects of the acids dumped into the harbors and they really didn’t care about dumping radiation into the water where civilians fish. One thing they found out fast was that copper piping tends to hold the radiation directly in the copper and so those systems had to be scrapped and all the copper piping had to be replaced.

In 1989 the EPA put out a report on the cleanup of Mare Island, Alameda Air station and Hunters Point and they state that they used samples that dug in 4 inches deep to determine radiation. They cleared all of these bases for nuclear radiation. Problem is that in order to fool a geiger counter all you need is a few feet of dirt. You can cover it up all you want, the radiation is still there. Also to test for Alpha and Beta Particles you have drill down and bring up a core of the materials which are them chemically separated to isolate the radioactive elements and then determine the radioactivity based on the contents, not a geiger counter.

Here is the official video of the project: https://archive.org/details/MISC1323OperationCrossroads1948
No description at the National Archives. Castle Films produced this film for the U.S. military — “Operation Crossroads” US Army film # MISC-1323 and US Navy film # MN 5345. Description from Armed Forces Films for Public and Television Use: “A documentary of the Able and Baker blasts of the Atomic Bomb Test at Bikini, produced by Joint Army-Navy Task Force One.”
National Archives Identifier: 88210 source file isn’t in the greatest shape.

Video detailing the Nuclear safety at the blast. Notice the officers checking the status of their geiger counters using a radiation source. Similar sources were found buried at San Francisco’s Treasure Island thus causing the site to become an EPA Superfund Nuclear Radiation Site.

Video link and information from Internet Archive. Uploaded by Periscope Films: https://archive.org/details/73862RadiologicalSafety