How is gaining experience calculated?

[RetLT]

Does anyone know the secret formula for how units gain experience in campaigns?

Is it just destruction of enemy units and if so does the value of the kill count (truck vs tank)?

Does clearing obstacles gain experience?

When it comes to artillery, does merely firing help?

And lastly, does getting shot at raise experience?

[Mobhack]

Experience is gained by surviving for a long time without getting (much) damage.

Low level experience (60s etc) is easier to gain than high value experts of 100+.

The first 5 or so kills are the best for upgrading, the rest dont matter much.

Clearing obstacles would do precisely nothing for anyone.

Artillery - is arty command, so OPs that call arty can gain. As can commanders that fire arty indirectly.

Getting shot at is bad, and can cause damage - which reduces the chance of gaining experience, especially if you get KO'd. Getting KO may leave a few crew - who aren't going to advance - or return you to a starter level for the era experience newbie crew if totally killed. Do - do not scout with bailed out crews!

Changing a unit drops experience - as the new kit needs getting used to.

[Imp]

Both firing & being fired on improve experience as does directing artillery.
Causing damage or killing something gains more, don't think target makes any difference.
Taking damage as infantry is okay so long as you deal out more than you take.
With vehicles if its damaged I would try to keep it safe unless needs dictate otherwise.