What does D 1-19 FA third Platoon stand for?

3rd Platoon, D Battery, 1st Battalion 19th Field Artillery Regiment which is a US Army unit.

I googled it. It is currently located at Fort Sill, Oklahoma. It is a Field Artillery training unit for soldiers after basic training. It is a part of the 434th Field Artillery Brigade. A soldier assigned to this unit is either a trainee or a trainer/support person.