The FTSE 100 defence manufacturer has been a little sluggish lately. It's a similar story for another FTSE 100 weapons maker, Babcock International Group. Still, that division is doing very nicely too, and so is the share price after yesterday's (30 July) results showed first-half revenues surging 26% to £11.3bn. Why is this FTSE 100 sector flying? Building tanks, fighter jets, ships and submarines is also a tough business, and BAE, Babcock and Rolls have all had technical issues over the years.