One of the first vessels outfitted for the test was , which had returned from its first survey voyage to South America, and was extensively rebuilt and refitted for the second survey voyage. As part of this work, "lightning-conductors, invented by Mr. Harris, were fixed in all the masts, the bowsprit, and even in the flying jib-boom." The captain, Robert FitzRoy, had been given command in the middle of the first expedition after the previous captain committed suicide. Before being given that command, FitzRoy had been a lieutenant on board HMS "Thetis" in Rio harbour when her foremast was struck by lightning. The "fore-topmast was shivered into a mere collection of splinters" and the foremast irreparably damaged, delaying the ship for almost two months while "the foremast was taken out afterwards, and replaced by another, purchased from the Brazilian government at a great expense."