IIRC the first U.S. H-bomb was a proof of concept device that used liquid deuterium and filled a large building. Nov. 1 1952. The Soviets tested a single stage bomb using lithium Aug 12 1953. The U.S..tested their first lithium fueled bomb Mar 1 1954. It was considerably more powerful than predicted & both scared the nearby monitoring team, & made a far bigger mess than expected. So, the U.S. was first with a fusion device, and technically the only actual Hydrogen bomb, that used Hydrogen. I don't think there's been a second. The Soviets were first to make a fusion device that used primarily Lithium, which is the type all subsequent "H-bombs" use. So... Technically, argue as you please. The Soviets beat the U.S. to a bomb that was even reasonable to deliver in something smaller that a Train or Ship. The U.S. beat the Soviets to a fusion explosion. However, the first sustained, repeatable, fusion reaction was by Philo T. Farsworth, ( the second most ripped off scientist in history ) 1964. This is in contrast to fission, which was first demonstrated with sustained, repeatable reactions in the first "reactor" in Chicago years before the Trinity test of the first Atom Bomb. Personally, I consider the Soviets first to a "practical" , "modern" Fusion bomb, while the U.S. Was first to demonstrate fusion in intended to be bomblike explosion form. But feel free to make up your own mind. I don't dispute first in having a bomb in operational form, since records from the Soviets are...unreliable. I will point out that keeping capabilities secret and lying about them is very traditional in military history. If as speculated, the Russian gov. is testing liquid fuelled fission rockets, then they are both behind the U.S. NERVA & DUMBO programs by decades, and well ahead of any unclassified U.S. program. PLUTO is one of the coolest flying things ever thankfully not flight tested. As a ramjet, it's range was limited only by the erosion of the reactor, with a theoretical range in days to weeks @ Mach 3. But Project Orion is IMHO the coolest flying machine thankfully never flight tested. See the book Project Orion by Dyson. https://www.amazon.com/Project-Orion-Story-Atomic-Spaceship/dp/0805059857 Probably the best fictional version. https://www.amazon.com/Footfall-Lar...5GWRN3WCZG7&psc=1&refRID=8E2MDQNRK5GWRN3WCZG7 Pluto, however, was ready to flight test, while Orion never had full scale hardware built... As far as you know.