In January 1871, Grant signed a joint resolution to send a commission to investigate annexation. For this undertaking, he chose three neutral parties, with Fredrick Douglass to head the commission. Although the commission approved its findings, the Senate remained opposed, forcing Grant to abandon further efforts. The stinging controversy over Santo Domingo overshadowed Grant's foreign diplomacy. American policy was to remain neutral during the Ten Years' War (1868–78), a series of long bloody revolts that were taking place in Cuba against Spanish rule. The U.S. refused to recognize the belligerence of the rebels, and in effect endorsed Spanish colonial rule there, while calling for the abolition of slavery in Cuba. This policy was shaken in October 1873, when a Spanish cruiser captured a merchant ship, "Virginius", flying the U.S. flag, carrying supplies and men to aid the insurrection. Spanish authorities executed the prisoners, including eight American citizens, and many Americans called for war with Spain. Grant ordered U.S. Navy Squadron warships to converge on Cuba, off of Key West, supported by the USS "Kansas". On November 27, Fish reached a diplomatic resolution in which Spain's president, Emilio Castelar y Ripoll, expressed his regret, surrendered the "Virginius" and the surviving captives. A year later, Spain paid a cash indemnity of $80,000 to the families of the executed Americans. In the face of strong opposition from Democrats, Grant and Fish secured a free trade treaty in 1875 with the Kingdom of Hawaii, incorporating the Pacific islands' sugar industry into the United States' economic sphere. Soon after taking office Grant took conservative steps to return the nation's currency to a more secure footing. During the Civil War, Congress had authorized the Treasury to issue banknotes that, unlike the rest of the currency, were not backed by gold or silver. The "greenback" notes, as they were known, were necessary to pay the unprecedented war debts, but they also caused inflation and forced gold-backed money out of circulation; Grant was determined to return the national economy to pre-war monetary standards. On March 18, 1869, he signed the Public Credit Act of 1869 that guaranteed bondholders would be repaid in "coin or its equivalent", while greenbacks would gradually be redeemed by the Treasury and replaced by notes backed by specie. The act committed the government to the full return of the gold standard within ten years. This followed a policy of "hard currency, economy and gradual reduction of the national debt."