HONOLULU -- A federal judge on Friday ruled the U.S. Navy must do more to protect marine mammals from the military's sonar training as it prepares to conduct training in Hawaiian waters next month.

Environmentalists are hailing Judge David Ezra's decision to grant a preliminary injunction in their suit against the government

Earthjustice is pleased with the ruling. However, Earthjustice officials said it did not go as far as they would like.

Navy ships use sonar to detect enemy submarines below. Starting next month, the military will have to modify its sonar exercises.

The judge ordered new "safety zones" to protect dolphins and whales in nearby waters.

"We are pleased that he recognizes that the military is not above the law," Earthjustice attorney Paul Achitoff said.

The judge's order also calls for the military to power down its sonar if a marine mammal is spotted within 1,500 meters of a ship. The signal must also be slowly ramped up to give marine life a chance to clear the area before the transmission is intensified.

The ruling also calls for additional aircraft to monitor the exercises. In the event an animal comes within 500 meters of a vessel, the sonar signal has to stop, the judge ruled.

"We had our own incident here where melon head whales were driven into Hanalei Bay and they had to be helped out of the bay by people who were there, and one calf actually died," Achitoff said.

In a written statement the military said that while the court acknowledges it is important to have a Navy ready to fight, the restrictions could seriously impact its ability to train.

"In ordering additional mitigation to reduce the risk to marine mammals, the order shifts the risk to sailors and Marines," Navy Capt. Scott Gureck of the U.S. Pacific Fleet said in the statement.

The Navy said it is weighing its legal options.

The Navy and will be back in court in April. The judge will look at whether there is a need for additional precautions.

The military has a series of sonar exercises planned over the next few years.