Complex sentence: Sufficient funding was not secured, and the Navy looked at the possibility of a fifth, and larger, Project 1143 carrier, modified to allow for Yak-141, MiG-29K and Su-27K operations.
Split into simpler sentences: Sufficient funding was not secured, and the Navy looked at the possibility of a fifth, and larger, Project 1143 carrier. This particular carrier would be modified to allow for Yak-141, MiG-29K and Su-27K operations.