PLT OF A C172 ENRTE TO A MIL PATROL INADVERTENTLY FLEW INTO CLASS D AIRSPACE DUE TO MARGINAL FLT VISIBILITY. THE RPTR CONTACTED THE TWR AND OBTAINED CLRNC TO TRANSIT THE AIRSPACE.

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THIS WAS A MIL FLT FOR PATROL OF SAN CLEMENTE ISLAND; A MIL FACILITY +/-50 MI W OF SAN DIEGO. FLT DEPARTED GILLESPIE FIELD (SEE) STRAIGHT OUT FOR THE COAST. IT IS NECESSARY TO PASS THROUGH MYF CLASS D AIRSPACE. UPON REACHING 1000 FT MSL; VISIBILITY BECAME MARGINAL. OBSERVER IN R SEAT (ALSO A PLT AND OWNER OF THE ACFT) WAS MONITORING CHART AND GPS TO KEEP ILS CLR OF CLASS B AND CLASS D AIRSPACE WHILE I FLEW AND WATCHED FOR TFC. DUE TO HAZE; VISIBILITY WAS POOR AND GND REFS WERE DIFFICULT TO SEE. WE WERE INTO CLASS D AIRSPACE BEFORE WE REALIZED IT. THE FAULT WAS ENTIRELY MINE. I SHOULD NOT HAVE RELIED ON THE OTHER OCCUPANT TO KEEP US CLR. THAT IS THE RESPONSIBILITY OF THE PIC. TO THE BEST OF MY KNOWLEDGE; THERE WERE NO CONFLICTS AND WHEN I ASKED THE CTLR WHETHER I HAD CAUSED ANY CONFLICTS HE STATED THAT THE SIT HAD INCREASED HIS WORKLOAD. IN RETROSPECT; DELEGATING NAV TO MY OBSERVER WAS A SERIOUS ERROR IN JUDGEMENT. IN FUTURE; I WILL HANDLE THE JOB MYSELF. SINCE MY ACFT IS BASED AT MYF AND WAS PREVIOUSLY AT SDM; I HAVE NOT HAD OCCASION TO FLY THIS RTE PREVIOUSLY. IN FUTURE; I WILL GET LCL INSTRUCTION BEFORE OPERATING VFR IN NEW AREAS OF CONGESTED CTLED AIRSPACE. IN THE PAST; I'VE MADE IT A PRACTICE TO OPERATE IFR IN THIS TYPE AIRSPACE TO AVOID THIS TYPE SIT. HOWEVER; THIS HAPPENED TO BE A VFR ACFT. SUBSEQUENT TO THIS INCIDENT I INITIATED A MEETING AND HAD A GOOD DISCUSSION WITH THE TWR SUPVR. THE AIRSPACE BOUNDARIES AND POTENTIAL PROBS OF ENCROACHMENT WERE DISCUSSED AND ARE MUCH BETTER UNDERSTOOD. TWR PERSONNEL WERE VERY ACCOMMODATING AND WILLING TO DISCUSS THESE TYPES OF SITS.