Service personnel took part in a parade and a service was held to remember those who died in conflicts.
Military flypasts were also held, while hundreds of bikers from across Europe converged on Alrewas to raise funds for the Royal British Legion.
Organisers said it attracted more people than last year's event, which 3,500 people attended.
Lt Col Alistair Fawcett, commanding officer of 22 Signal Regiment, said it was a chance for people to show their support and offered a moment to reflect on the various conflicts around the world.
Similar events have been taking place across the country and several of them have seen heightened security after recent attacks in Tunisia, France and Kuwait.
Thousands of people have marked Armed Forces Day at the National Memorial Arboretum in Staffordshire.