Basic dimensions for all of the Sea-King variants started out exactly the same. The SH-3H upgraded model utilizes a 4 inch longer tail pylon, permitting the use of the longer tail rotor blades, thus improving tail rotor performance just like the commercial S61N model.
The HH-3E (S61R) is a slighty longer airframe than the H-3, and is the basic design for the current "stretch" SH-3 (prospective S61T) because all the parts like flight controls, etc, already exist.
The commercial S61N and S61L both had stretched airframes, with plugs behind the cockpit, to provide more cabin space, and a range of cargo or airstair door configurations, but more importantly to remedy a serious aft C of G limitation with the basic design. The "L" model had the same short tail pylon as the H-3, whereas the "N" model had a longer pylon, and various changes to the tail rotor drive-train and stabilizer.
I was never CAF, but am intimately familiar with all variants.
The basic Agusta versions were straight licence built Sikorsky SH-3D models, and everything on them is identical to a Sikorsky built model. Agusta also built a large number of HH-3 models. Agusta's licence territory covered Southern Europe, North Africa, Middle East and South America. Many remain in service.
Concur with the naming convention of the US Navy helicopters - the basic protocol originated with the Navy (same for the Army with Native American tribes).
The Agusta S61N1 Silver was a short S61 (SH-3D length) commercial S61N helicopter. The timing was wrong; if they had started building them 5 years earlier and incorporated some significant upgrades, it would probably have been a raging success - but they didn't. Two helicopters were ever built and both were sold to, and are still operated by the Royal Malaysian Air Force.
