Worried about collateral damage to whales, dolphins and other marine life, environmentalists are fighting the U.S. Navy in court in a bid to protect the creatures of the sea from war games in the Pacific Ocean -- while the Navy insists their claims are overblown and the exercises are necessary and safe. 

U.S. Navy testing and war games are underway in American waters off the coasts of California and Hawaii. The drills amount to critical practice for the military and last through 2018, but environmental groups like EarthJustice say hundreds of marine mammals will die or get injured by the time the Navy is through. 

"The worst harm comes from the explosives going off," said David Henkin, an attorney for EarthJustice. He and others say they don't want to stop the Navy from training -- but change how they do it. 

The testing areas are home to nearly 40 marine mammal and five sea turtle species. According to the Natural Resources Defense Council, the Navy will conduct 500,000 hours of sonar testing between 2013 and 2018. During that time, 260,000 bombs, missiles and other explosives will be tested. 

According to an analysis of the National Marine Fisheries Service, a division of the Department of Commerce charged with protecting mammals, the estimated damage to the marine life includes the deaths of 155 whales, dolphins and seals; 2,000 permanent injuries to marine mammals; and 9.6 million incidents of temporary hearing loss and behavior changes in areas like migration, nursing and feeding. 

But the Navy is fighting back and argues that war-gaming, which dates back to 1886, is a consistently reliable way to train for combat.

“Despite decades of the Navy conducting very similar activities in these same areas, there is no evidence of these types of impacts,” Kenneth Hess, Navy spokesman, told FoxNews.com. “Bear in mind that the permits the Navy requires to conduct at-sea training and testing can only be issued if our activities will have no more than a negligible impact on marine mammal populations.”

Hess also stressed that the number of marine mammal injuries and deaths estimated in the Navy’s planning documents cover a five-year period "and represent the worst-case scenarios.”

The games have been played out in the Hawaii-Southern California Training and Testing Study Area for more than four decades – and environmentalists have been trying almost just as long to stop them.

For more than a decade, the Natural Resources Defense Council has been suing the U.S. Navy over its use of high-intensity military sonar during training exercises.

Last year, the Conservation Council for Hawaii filed a federal lawsuit against the National Marine Fisheries Service, the Department of Commerce and the Navy. The group submitted a motion last week asking a judge to declare the games illegal because they violate a law meant to protect endangered mammals.

“The area in which the Navy conducts its research is the size of all 50 U.S. states combined,” said Henkin, who is working on behalf of the conservation council. 

He has submitted a quarter of a million documents to support his case and says the Navy’s training plans threaten entire populations of marine wildlife off the East Coast, southern California, Hawaii and the Gulf Coast. Blue, fin and humpback whales are among those in danger, he said.

Henkin said he wants the Navy to change the times it conducts war games -- altering the dates by just a few weeks in some cases, he said, would protect some of the endangered species. The frustration, environmentalists told FoxNews.com, stems from the Navy's alleged refusal to compromise. 

“The Navy blankets the entire ocean floor with high levels of noise,” Henkin said. “[Whales and dolphins] can’t communicate, can’t feed and in many cases, undergo constant bombardment." 

In 2013, the Navy also rejected California Coastal Commission suggestions that would limit sonar training to avoid harming whales and other marine mammals. 

A year before that, a coalition of Native American groups sued the National Marine Fisheries Services for not protecting thousands of whales, dolphins, seals and sea lions from the warfare training exercises along the coasts of Oregon, California and Washington state.

The U.S. Supreme Court got involved in 2008 and sided with the Navy, ruling that sacrifices needed to be made in the military’s push to protect the public.  

Naval war games prepare participants for war by testing personnel, tactics, procedures and equipment -- and they date back decades. 

By the time of the Pearl Harbor attack, all but one wartime admiral and the entire U.S. Navy leadership had participated in war games. By the mid-2000s, the Navy started working on a three-dimension naval tactical warfare simulator called Kill Chain. The program was funded to $11.4 million in 2007, with an initial emphasis on anti-submarine warfare.

Aside from the lawsuits, there have been multiple attempts to force the Navy to alter how it conducts its testing. There’s even a petition on MoveOn.org titled “Stop the Navy’s War on Whales and Dolphins Now!” which claims the U.S. Fisheries service ignored warnings and “rubber-stamped the Navy’s request and issues the permits anyway.”

“Now is the time for us to go directly to the top of the command chain and demand that the President invoke his constitutional powers to stop this senseless slaughter,” the petition reads.

So far, more than 70,000 people have signed the petition.