This year’s Rim of the Pacific naval exercise will feature a larger group of participating countries seeking to develop better maritime cooperation, Navy Adm. Jonathan W. Greenert, chief of naval operations, told Pentagon reporters today.

“We’ve been doing RIMPAC for over 40 years now, and this year is different because it’s bigger,” Greenert said. “We have somewhere on the order of 42 ships … from 22 countries here this year. Twelve of them will bring units, and that’s sort of extraordinary.”

The RIMPAC exercise, hosted by the U.S. Pacific Fleet, is the world’s largest international maritime exercise, according to its website. The exercise, which begins June 29, is the 23rd in a series that began in 1971.

“RIMPAC provides a unique training opportunity that helps participants foster and sustain the cooperative relationships that are critical to ensuring the safety of sea lanes and security on the world’s oceans,” the website states.

Greenert noted the 12 countries providing units at RIMPAC 2012 will include ships, some aircraft and even submarines.

The United States, Russia, Peru, Canada, Australia, Japan, India, France, South Korea, Malaysia, Singapore, Indonesia are among the 20-plus nations taking part in the exercise, Greenert said.

“So we’ve got really a worldwide exercise here,” Greenert said.

The admiral said this year’s exercise will also feature vessels using biofuel. The Navy has experimented with biofuel consisting of a 50/50 mix of regular petroleum fuel and algae-derived, hydro-processed oil.

“What is different about RIMPAC? Well, we will have a carrier strike group there with the carrier, the [guided missile destroyers], and the supporting ship operating on biofuel,” Greenert said.