Hi all,

I would like to ask for help with explanation of phrases I have found to be used very often in several Coastal Command ORBs in erly months of 1945:

1. "on patrol using 5 NM vis. Area covered 2 times"
I suppose the patrol track has been folwn twice but what about the first phrase? It evokes me "visbility" but as nearly always there is value 5 NM (what I expect means nautical miles), sometimes as "using 5 miles visibility" I came to the conclusion it was 5 NM range used on the radar during the patrol. Am I right or totally wrong?

2. "Efficiency 90%. Radar has been used continuously"
The second expression is clear, but what means the first one? The value varies from abotu 75 to 95%. Some kind of radar efficiency? How it was established?

Any help wich explanations would be much appreciated.