Runners who took part in the Boston Marathon April 21, and the thousands of spectators who watched them, received an additional boost of protection from members of the Massachusetts, Maine, and Rhode Island National Guards. More than 800 members from those states supplemented civilian law-enforcement agencies along the 26.2-mile route. They were trained in multiple disciplines, including chemical, biological, radiological and nuclear detection, health care, and security. The Massachusetts Guard’s 79th Troop Command coordinated operations among the Guard units, local police departments, and the Boston Athletic Association, which sponsors the event. The added security aimed at staving off any recurrence of the tragedy that occurred last year, when two brothers detonated makeshift explosives at the finish line. Three people died and more than 250 others were injured.