There were a lot of S.H.I.E.L.D. agents in The Avengers, not to mention the military presence on the street during the Chitauri attack. Despite the fact that many of those scenes were ultimately cut from the movie, you have to hand it to Whedon for looking to bring some realism and authenticity to the production. He enlisted Army Reserve soldiers assigned to the 391s Military Police Battalion for these in order to lend their moments some credibility, ensuring that the military actually acted like the military rather than having actors and extras make the kind of mistakes that those in service often criticise in movies.
