[hyperion2206]

Originally Posted by rrmelend

I'd like to see your sources for this info. You are right abou the Barb but most of the skippers running on the top for extended periods of daylight hours came during the last year of the war when radar had advanced enough and the threat of detection was less than before.

I thought the same as you rrmelend until I read the patrol logs of the USS Gunnel. In 1944 they found out that around the Japanes mainland there were many radar stations and a lot of Japanese ships had radar on board as well. I doubt that the Japanes radar was as effective as the US radars but Japanese radar was jamming the radar of the Gunnel. Although Japanese radar might not have picked up the Gunnel it certainly neutralized Gunnels capability to pick up Japanese shipping.
For example:

2240 (H): S.J.Radar contact, position Lat. 01° - 32.5' N., Long. 120° - 46' E. bearing 243° (T), distance 21,500 yards. The next morning periscope observation disclosed these to be four medium sized tankers escorted by four destroyers. Radar tracking gave target base course of 090° (T), speed 12 knots. They zigged from 060° (T) to 120° (T) about six minutes on each leg. First I tried to close these targets on the port bow, then on the flank, and finally on the port quarter. Each attempt at closing resulted in an escort placing itself between the submarine and the major targets, thus frustrating these endeavors to gain an attack position. There was definite radar interference from the escorts and had been since initial contact. Therefore in tracking, the transmitter was energized at irregular intervals to obtain data for the plotting party.

Taken from this site: http://jmlavelle.com/gunnel/patrol4.htm