Well, that would be the II'ya Muromets. The production follow on to the Grand, if you will. You can find out a lot of Igor Sikorsky history right from the Sikorsky homepage, which will bring you here:
http://www.sikorsky.com/frames/exter...kyarchives.com
An amazing man. An aviation pioneer in fixed wing and rotary wing aircraft. A deeply spiritual man. A man both intelligent and humble. Lots of good books on Mr. Sikorsky.
One of the best I've read and enjoyed is:
Igor Sikorsky – His Three Careers in Aviation, by Delear, published by Dodd, Mead and Co., 1969
-- IFMU