There were many advances and new designs in gunpowder weapons during the beginning of the dynasty, but by the mid to late Ming the Chinese began to frequently employ European-style artillery and firearms. The "Huolongjing", compiled by Jiao Yu and Liu Bowen sometime before the latter's death on 16 May 1375 (with a preface added by Jiao in 1412), featured many types of cutting-edge gunpowder weaponry for the time. This includes hollow, gunpowder-filled exploding cannonballs, land mines that used a complex trigger mechanism of falling weights, pins, and a steel wheellock to ignite the train of fuses, naval mines, fin-mounted winged rockets for aerodynamic control, multistage rockets propelled by booster rockets before igniting a swarm of smaller rockets issuing forth from the end of the missile (shaped like a dragon's head), and hand cannons that had up to ten barrels.