St. Peter's Chapel, Mare Island (locally, St. Peter's Chapel) is an historic church building located on Walnut near Cedar Avenues, Vallejo, Solano County, California, in the historic core of the Mare Island Naval Shipyard. It is the first Naval chapel in the Pacific, the first interdenominational chapel in the armed services, and the second chapel built on a U.S. Navy property, the first being the original Naval chapel in Annapolis replaced in 1904.

Dedicated on 13 October 1901, St. Peter's Chapel is the oldest extant Naval chapel in the United States and has one of the largest collection of Tiffany windows in situ under one roof. It is "a key contributing element of the Mare Island Historic District, listed in the National Register of Historic Places and a National Historic Landmark, and individually, as one of the most important chapels owned by the U.S. Navy."

The person most responsible for the presence of St. Peter's Chapel at Mare Island was Rev. Adam A. McAlister (1841-1916), chaplain in the U.S. Navy from 1873 to 1909, serving almost all of those years at Mare Island. During the decades he served before the chapel was built, he would hold services at whatever space could be "rigged for church" with minimal disruption to ordinary functions. Not satisfied with this makeshift arrangement, McAlister was able to convince his friend U.S. Senator George C. Perkins to include a $5000 appropriation in the 1900 Naval Appropriations Act for the construction of a chapel at Mare Island.

McAlister quickly hired San Francisco architect, Albert Sutton, to draw up plans for a chapel at Mare Island, paid him $50 from church donations for his services, and forwarded Sutton's plans to the Navy Department in Washington, D.C. on 30 November 1900, only months after the congressional appropriation. The chapel was largely completed in 1901, had its first service on 6 October 1901, was dedicated on 13 October 1901 by various Protestant clergies, followed a month later by its first Catholic mass. Interdenominational from its beginning, St. Peter's Chapel was named after Simon, called Peter, a toiler of the sea whose story is told in the Gospels.

Over the next decades, art glass windows and many of the interior furnishings were added and paid for by parishioners and private contributions. The stained glass windows were typically donated by family members in memory of U.S. Navy personnel; commemorative ceiling and wall tablets were likewise dedicated to various individuals and groups. Through the efforts of Chaplain McAlister and his friends, St. Peter's became an important U.S. Navy memorial chapel. Almost all of the art glass windows were in place by McAlister's funeral at St. Peter's Chapel in 1916.

"That the chaplain and his friends have been successful is attested by the many who come almost daily and sit for an hour in the chapel studying the works of art and receiving the spiritual uplift..."

The chapel served the Mare Island community — Naval and Marine officers, enlisted men and women, as well as the civilian workforce — much like a local community church, given how isolated and self-contained Mare Island was then. It was a focus of life on the base, with the art glass windows and commemorative tablets contributed by the community reflecting the sense of community and continuity that existed at the base through its numerous decades of service. For many generations, it was the site for various key transitional events, like weddings, baptisms, and funerals. World War II brought the greatest number of weddings to the chapel, as young sailors got married just before being sent off to the Pacific Theater. As historian McDonald noted, "The chapel, more than any other building, bears witness to the closeness of the community that developed at the Mare Island Naval Shipyard."

Over 300 persons crowded into the chapel on Christmas Eve of 1995 for the last scheduled service before the closure of the base on 31 March 1996. The fourth and last advent candle was lit by Captain Cavender, the last Shipyard Commander, and his wife. As it was for numerous decades, the last scheduled service at St. Peter's Chapel ended with the singing of the Navy hymn, Eternal Father, Strong to Save.