When inventory returns exposed a dangerous shortage of gunpowder, Washington asked for new sources. British arsenals were raided (including some in the West Indies) and some manufacturing was attempted; a barely adequate supply (about 2.5 million pounds) was obtained by the end of 1776, mostly from France. In search of heavy weapons, he sent Henry Knox on an expedition to Fort Ticonderoga to retrieve cannons that had been captured there. He resisted repeated calls from Congress to launch attacks against the British in Boston, calling war councils that supported the decisions against such action. Before the Continental Navy was established in November 1775 he, without Congressional authorization, began arming a "secret navy" to prey on poorly protected British transports and supply ships. When Congress authorized an invasion of Quebec, Washington authorized Benedict Arnold to lead a force from Cambridge to Quebec City through the wilderness of present-day Maine.