The U.S. Navy’s association with Guam began in 1898 at the height of the Spanish-American War. Not long after the victory of the U.S. Asiatic Squadron over a Spanish squadron at Manila Bay on 1 May, three U.S. troop transport ships carrying the first Philippine Expeditionary Forces steamed out of San Francisco on 25 May 1898 and rendezvoused with the cruiser Charleston (C-2) under the command of Captain Henry Glass, USN. In Honolulu, Captain Glass opened sealed orders from Secretary of the Navy John D. Long ordering him and his force to stop at the Spanish island of Guam en route to the Philippines, and “use such force as may be necessary to capture the port.”
When Charleston entered Agaña Bay on 20 June, the crew anticipated a cannonade from Fort Santiago but the guns were silent. Captain Glass steamed further into the harbor and began bombarding Fort Santa Cruz but received no response. A large group of curious residents congregated at the port to welcome the ship. Unaware that the two countries were at war, they believed the Charleston was saluting the fort on a state visit. After a couple days of political negotiations, the Spanish governor, Marina Vega, surrendered the garrison. Captain Glass entrusted the governance of the island to an American citizen named Francisco Portusach until U.S. reinforcements could arrive.
Historians are generally in agreement with this part of the story but what happened next is subject to debate. The popular narrative is that Francisco Portusach, a naturalized American merchant living on Guam, became the first American governor of the island before being deposed by the Spanish treasurer, José Sixto (also spelled “Sisto”), shortly thereafter. Guam’s politics after American capture were far more complicated than this narrative suggests. Far from being the first American governor of the island, what little evidence exists indicates that Portusach balanced power during this period with Sixto in an informal governing arrangement. This arrangement was convenient for both Portusach and Sixto because it allowed both to continue working in their former jobs after Guam’s capture, but was not a long-term solution. The roughly yearlong period of political ambiguity ended in August of 1899 when Captain Richard Leary, USN, established the first naval administration of Guam.
Francisco Portusach was a Spanish-born whaler and merchant naturalized as a U.S. citizen in 1888, and informally made the administrator of Guam on 22 June 22 1898, by Captain Henry Glass, USN, before Glass departed for Manila. While various popular sources list Portusach as the first governor, no formal record of this exists and historians have relied on Portusach's own recollection of a verbal agreement made between him and Captain Glass. Portusach’s account was published in the U.S. Naval Institute Proceedings in 1917, 19 years after the events transpired. Even in his own account, Portusach never claimed to have been governor of Guam. Rather, he stated that Captain Glass asked him to “take care of the island” until U.S. reinforcements could arrive. Unfortunately, Captain Glass did not issue any written authorization to legitimize Portusach’s authority. Portusach noted in his account that this proved problematic multiple times, as Spanish treasurer Jose Sixto, who was not taken prisoner by the U.S. because he was a civilian, disputed Portusach’s authority based on lack of written authorization.
After Glass departed Guam, Sixto refused to surrender the island’s treasury to Portusach. In the absence of any American Sailors or Marines and nothing in writing supporting Portusach’s claim to power, Sixto simply continued paying Spanish bureaucrats and militia members, which consolidated his influence over the island. In the year-long vacuum left by the United States, Sixto bankrupted the treasury and allowed a breakdown of law and order, which was manifest in riots between Chamorros (native Guamanians) and Filipinos. In the months following Guam’s capture in June, Portusach continued supplying various ships and partially fulfilled his duties by organizing the construction of a road, but was not able to challenge Sixto’s control of appropriations for fear of reprisal. By the same token, Sixto, according to Portusach’s account, was equally apprehensive about taking down the American flag and making a full effort to reassert Spanish control. Conflict between pro-American and pro-Spanish Guamanians was manifest in Portusach and Sixto’s contentious relationship. While Sixto did verbally threaten Portusach on several occasions, tension never escalated into bloodshed. Portusach continued to profit from supplying passing ships and improved island infrastructure and Sixto did not surrender control of the island’s funds and continued to pay local militia. Portusach’s account suggests that no one was explicitly “governor,” but each man’s power ebbed and flowed as they resumed their normal activities.
In January 1899, the collier Brutus (AC-15) under the command of Lieutenant Vincendon L. Cottman, USN, entered Guam and gave control to Don Joaquin Perez, who was a judge during Spanish rule, after a meeting with influential Guamanians including Portusach and Sixto. In his account, Portusach implied that he advised Cottman to appoint someone other than himself, as he had “so much business to attend.” Brutus was followed by the gunboat Bennington (PG-4) under Captain Edward D. Taussig, USN, which carried vital information regarding the Treaty of Paris stipulating Guam’s political fate. Under Taussig, American authority was reasserted, but Perez remained in charge of the island until the collier Nanshan (AG-3) arrived and Ensign Louis A. Kaiser, USN, became acting governor. On 7 August 1899, Captain Richard Leary, USN, landed in Guam and became the first naval governor, thus ending this confusing period in the political history of Guam. The U.S. Navy continued to govern Guam until 1950, with a three-year hiatus when the island was captured by Japan in 1941.
— Marcus J. Thompson, Naval History and Heritage Command, June 2017
 Leslie W. Walker, Guam's Seizure by the United States in 1898, Pacific Historical Review, Vol. 14, No. 1 (Mar., 1945), 11.
 See Robert F. Rogers, Destiny's Landfall: A History of Guam, (Honolulu: University of Hawaii Press, 1995), 110−117; and Walker, 11.
 Robert F. Rogers, Destiny's Landfall: A History of Guam, (Honolulu: University of Hawaii Press, 1995), 114.
 Walker, 7−8.
 Francisco Portusach, History of the Capture of Guam by the United States Man-of-War Charleston and its Transport, United States Naval Institute Proceedings, Vol. 43, No. 4, (Annapolis: U.S. Naval Institute, April 1917), 707.
 Portusach, 710.
 Portusach, 711.
 Portusach, 711.
 Portusach, 715.
 Portusach, 716.
 Portusach, 717.
 Rogers, 116−117.
 Rogers, 114.