Maryland Form 502SU

The Code P subtraction is for military active duty pay ($15,000 or less) earned while serving overseas for MD residents. Couples filing joint returns can get a deduction for each spouse that meets the requirements.  To claim the deduction you must enter an active duty military W2 (in your case one for each of you) in the federal interview and after entering the form information you will arrive at the page asking for "Uncommon Situations".  There you would need to select "Active Duty Military" for each of the W2s.  Finally, in the MD interview in the "Income" section, you would need to enter an amount in the Military Wages Earned Overseas box when asked.  

If you do not meet the requirements for the deduction go back to the above steps and "Edit" the place that does not apply to you.  For example if you have active military pays, but none was earned overseas, "Edit" your MD interview, "Update" the "Income" section and blank out/zero the "Military Wages Earned Overseas" box when asked.  

If you are working in a desktop product then in the forms mode open the MD "Info Worksheet" and scroll to the "Military information" section. Box 1b(1) is an entry box that you can blank out to get rid of the deduction as well without an override.