that is excellent timing for someone that are no longer in the
army. 
in terms of training for 1/2M, i suggest u get some training books
on Marathon or from the webby, go through it and see how the actual
ways of training should be...
what the army teaches you for 1/2M brings you to a certain level.
What happens after(if you want to improve further)), you have to do
much more. I have not been trained in the Army on 1/2M before, but
i guess the training is different from what other(serious runner)
is doing.
Basically 1 week(7 days), runs for 6 days and i day rest. mixture
of interval training, fartlek, long distance running, easy run,
cross training(swim/cycle/gym), tempo run etc. 
so far, i experience on a few times when heartbeat not returning to
resting rate after a long run(basically on races) and i feel
terrible. Basically i attribute it to no proper warm down. After
chiong the last part of the race/run, we are suppose to jog slowly
for a few minutes to slow down, but we tend to choose walking
instead, which is not recommended. A sudden stop in activities, the
heart cant take it and the heart rate will remains high. 
After a run, ur heart rate should drop to normal rate within
10mins. If it takes more than 10 mins, it means you had push too
hard during the run. If you still about 70-80% after 30mins, you
better find a place to rest or seek help. Take more water and find
a cool place to rest. For me, if my heart rate dont reduce 5mins
after the run, i will find a place to rest immediately.
