I was sorry to have missed the two papers by Captain K. D. Jones and Mr P. J. Houseley on the above subject, presented at a recent meeting of the Institute, and the subsequent discussion. Fortunately both Captain Jones and Mr. Houseley have been kind enough to let me see copies of their papers and I would like to add two pieces of information which may be of interest with reference to Captain Jones's paper.

The first is in regard to the making of ‘the first decision’ in clear weather. Captain Jones says that most mariners on sighting a target decide on the risk, or the probable miss distance, by an accurate even if intuitive evaluation of aspect and range. (They must also take into account the relative bearing of the target and its speed relative to that of own ship.) For the purposes of his argument Captain Jones omits from the clear weather case the alternative method of using radar in assessing the risk or probable miss distance. Evidence on the comparative accuracies of these two methods may be of interest; a series of demonstration runs on the Predictor automatic plotting radar in Elettra lll in the English Channel provided an opportunity to obtain some such evidence.

On one occasion which I have in mind, under conditions of clear visibility in daylight, a ship estimated at about 2000 tons was seen about 45° off the port bow at a (radar) range of 7 miles in a crossing situation.