PHIPPSBURG — The second Zumwalt-class stealth destroyer built by Bath Iron Works cruised down the Kennebec River Monday afternoon for the ship’s first tests in the open ocean.

A crowd of several hundred people, including BIW employees and dozens of Navy crew members, waved and snapped pictures as the future USS Michael Monsoor passed the southern tip of Phippsburg just before 1 p.m. With its sharply angular hull and deckhouse, the futuristic-looking warship contrasted with the stone walls of Fort Popham as the 610-foot-long ship exited the Kennebec and headed toward the Gulf of Maine.

“It’s really exciting, and it’s breathtaking to see it,” said Carl Pinkham as he watched the guided missile destroyer he helped build steam toward the Gulf of Maine, accompanied by the Coast Guard, security boats and tugboats. Pinkham had gathered near Fort Popham with about a half-dozen other “preservation technicians” from BIW who perform the nonstop painting, sandblasting and other maintenance needed on destroyers under construction in Bath.

“It took awhile to get from where we started to where it is now,” Pinkham said.

Fabrication of the Monsoor began in 2010, with the keel-laying ceremony taking place in May 2013 and the christening held last June. Sea trials are the first major test of the high-tech ship before a Navy inspection team conducts additional at-sea testing early next year.

“Michael Monsoor (DDG 1001) is currently on Builders Trials, testing the hull, mechanical and engineering components of the ship,” Bath Iron Works said in a statement. “While all these systems are tested pierside, there is no substitute for the real world testing taking place in the Gulf of Maine.”

The ship is named for Petty Officer 2nd Class Michael Monsoor, a Navy SEAL who was killed in Iraq in 2006 when he covered a grenade with his body to shield others from the blast. Monsoor was posthumously awarded the Medal of Honor by President George W. Bush.

Neither BIW nor the Navy released details of the Monsoor’s transit down the Kennebec or its travels around the Gulf of Maine for security purposes. The first Zumwalt-class destroyer, the USS Zumwalt, docked in Portland Harbor during its week-long sea trials in order to resupply and exchange passengers or crew.

Deborah Dow and Ed Cleary had no idea the ship would be passing by when they planned their traditional trip to Popham from Vassalboro on Monday. The two were impressed by the sight of the unusual ship.

“It’s amazing,” said Dow. “It was a nice surprise.”

It was sunny with temperatures in the upper 30s on Monday afternoon, although gusting winds gave the air a bite. There were noticeably fewer spectators at Popham on Monday for the Monsoor compared to the first transit of its predecessor, the USS Zumwalt, almost exactly two years earlier. But dozens of uniformed Monsoor crew members – who were not part of the first stage of the builder’s trials – gathered on the beach to pose for pictures of the passing ship and then wave to those on board.

BIW, which is owned by General Dynamics, currently has six destroyers at various stages of construction in its Bath shipyard: two Zumwalt-class stealth destroyers and four of the Arleigh Burke-class destroyers that have provided guided missile capabilities around the globe.

The Zumwalts are the largest and most technologically advanced destroyers ever built for the Navy. They are designed to appear as much smaller vessels on radar thanks to their smooth exterior surfaces, “tumblehome” hull and other design features. While they are significantly larger than Arleigh Burke-class destroyers, automation will allow the Zumwalts to operate with half the crew of the other class. Zumwalts are also regarded as technological showcases for future ships in terms of their all-electric powerhouse and weaponry.

All of that technology comes at a cost, however. The Congressional Research Service has estimated that each of the three ships will cost more than $4 billion to construct, compared to about $1.6 billion for Arleigh Burke-class destroyers.

The first ship of the class, the USS Zumwalt, was delivered to the Navy in May 2016 but experienced several high-profile mechanical failures, including one incident while transiting the Panama Canal. Experts said mechanical and technological problems are anticipated in the first ship of a new class, however.

The USS Zumwalt is currently being outfitted with its weapons and other systems at its home base in San Diego.