A song with the same title:

Knock On The Door

They say you always know, somehow you can be sure
Even when it comes at dead of night, you can tell that knock on the door
The clothes they wear are black, these messengers of war
They quickly give their news then disappear, when you hear that knock on the door.
And I try to remember what he was like, how did he feel inside
The taste of his kiss, have I forgotten all this?
Why wasn't it him at the door? At the door...
My days are dark with dreams, scenes of horror, death and gore
I think about him lying in the desert there, since I heard that knock on the door.
My friends have rallied round, their love I can't ignore
They do the shopping wake me up each afternoon, since I heard that knock on the door.
And I try etc.
I've kept his uniform, his medals in a cupboard drawer
There's nothing else just wedding cards and photographs, since I heard that knock on the door
I feel so lost alone, when evening comes I miss him more
I reach out try to touch him in my empty bed, since I heard that knock on the door.
And I try etc.
I hear the bugles play, watch poppies flutter to the floor
November's always waiting for those aching hearts that have heard that knock on the door.
But still the wars go on, sometimes I wonder what they're for
But peace is one thing no-one ever understands 'til they've heard that knock on the door.
And I try etc.