On the problem of search with ships and aircraft

After World War II, B. O. Koopman published the series of three papers on the theory of search where the search is carried out with aircraft (or ships) only. However, in the case of emergency, it seems to be reasonable that the search is carried out not only with aircraft but also with ships. In this paper, we extend Koopman's model and consider the problem of search with ships and aircraft. By solving the problem in polynomial time, we expect that our results will contribute to the theory of search.