The Kick 'em Jenny volcano, 6 miles north of the island, began erupting in 1939, when it spit an 886-foot cloud of ash into the sky above the water. Since then it has erupted more mildly at least 12 times.
Ships are banned within 1 mile of the volcano, which in an eruption can stir up high waves and heat surrounding waters to boiling temperatures.
The scientists began their weeklong visit Thursday, using the small submarine resistant to high temperatures in a series of dives, scientists said.
"We now have a unique opportunity to get into the crater of this active volcano without risking our lives," said the project's chief scientists, Haraldur Sigurdsson, of the University of Rhode Island, working with scientists from the Trinidad campus of the University of the West Indies.
During the expedition, the scientists plan to map the area topographically, take earth samples from its cone, record seismic data and study nearby animal and plant life, Sigurdsson said.
The research is to be posted on NASA's Distance Learning Web site.
Kick 'em Jenny is the only active underwater volcano in the Caribbean, though there is one other erupting volcano on the British Caribbean island of Montserrat. The Soufriere Hills volcano stirred to life in 1995 and has since buried many southern parts of the island, including the capital of Plymouth.
Scientists originally feared Kick 'em Jenny was growing toward the water's surface, and that large eruptions eventually could cause tidal waves.
In 2002, however, a group of scientists discovered that though the summit is just 560 feet underwater, the volcano is venting farther down on the mountain at 880 feet. Researchers say they don't expect the volcano to break the surface and form a new volcanic island any time soon.
The volcano's last major eruption began Dec. 4, 2001, and lasted two days. Although nothing was detected at the water's surface, earthquakes were felt throughout northern Grenada.
The scientists are working on a $283,000 grant from the U.S. National Oceanic and Atmospheric Administration, Sigurdsson said.