However long you have done, if you leave before your Immediate Pension Point you will have a preserved pension to be paid at some point in the future (depending on the scheme you are on). You may get a lump sum, again depending on which scheme you are a member of. I'd suggest you got to your pay staff and ask for one of the several leaflets that explain in some detail what your pension is all about. You could also consider the Forces Pension Society for advice. Asking here 'wud I still get my half pension?' is hardly going to get you the information you require to make a decision that effects your entire future life.
Also don't forget if you go into the police and some other public service work you can transfer your pension, I'm sure all that will be explained if you follow Devs advice. Just bear in mind that's a lot of service to transfer.
Seriously popaz. Seek financial and pension advice from those in the know. You're unlikely to get sound advice from complete strangers.
Take Dev's advice; Get advice. Research. And do the number crunching.