Staff Writer (Updated: 11/20/2014):
The H-4 proved serviceable enough but it was not void of issues from a military perspective - such service introducing a level of rigors not common to commercial-minded travel. The H-4s were found to have rather weak hulls for consistently rough operations and their engines were weak in powering the large airframe - pilots were none too fond of the model and let it be known.
Porte moved to evolve the H-4 into a more viable military-minded product and used several H-4 airframes to test various outfits and arrangements. Work begat the Felixstowe F.1 of which four were built and these aircraft involved revised Porte-designed hulls as well as 2 x Hispano-Suiza 8 series engines of 150 horsepower (each) while retaining the tail section and biplane wing of the H-4. Waterborne performance was dramatically improved and testing showcased a more sound design than before.
Work continued by Porte, now focused on bringing a modified Curtiss H-12 aircraft to a Royal Navy standard. The H-12 was a dimensionally larger system and saw its first flight in June of 1914. Some 478 of the type would be built before the end and both the United States and United Kingdom would take the aircraft into their respective inventories. Again the same limitations of the H-4 were encountered in the H-12 but the already-completed work on the former helped to usher in a revised design for the latter producing the Felixstowe F.2. Changes included use of a Porte-designed hull with the wings of the Curtiss H-12 though an all-new tail section was added and power came through 2 x Rolls-Royce "Eagle" series engines. First flight of the F.2 was recorded in July of 1916.