Sentence:  The 12,000-pound ‘<WSD>Tallboy</WSD>' was another creation from Barnes Wallis, who had long been privately working on the new generation of heavyweight, aerodynamic bombs....Reaching a terminal velocity or 3,700 feet per second, the <WSD>Tallboy</WSD> was capable of making a crater that would have taken 5,000 tons of earth to fill. 
Meaning of the word marked with <WSD> tags:  An (earthquake bomb) developed for the (British Armed Forces) and deployed by the RAF during World War II.