Some early Vibrolas on Rickenbacker guitars were not operated by hand, but rather moved with an electrical mechanism developed by Doc Kauffman to simulate the pitch manipulation available with steel guitars. The Vibrola distributed as an option with Rickenbacker Electro Spanish guitars was hand operated like the earliest Epiphone Vibrolas. A later unit was created and used on Rickenbacker's Capri line of guitars in the 1950s, such as John Lennon's 1958 Rickenbacker 325. It was a side-to-side action vibrato unit (rather than the up-down action of later units) that was notorious for throwing the guitar out of tune, hence Lennon's replacing his with a Bigsby B5 unit (Lennon's 1964 Rickenbacker 325 came fitted with a Rickenbacker Ac'cent vibrato unit). Bigsby The first commercially successful vibrato system for guitar was the Bigsby vibrato tailpiece, often just called a Bigsby, invented by Paul Bigsby (US Patent D169120 filed in 1952, issued in 1953). The exact date of its first availability is uncertain, as Bigsby kept few records, but it was on Bigsby-built guitars photographed in 1952, in what became its standard form. In several interviews, the late Merle Travis, for whom Bigsby designed his first vibrato, recalled the prototype as being built for him in the "late '40s". The design uses a spring-loaded arm that rotates a cylindrical bar in the tailpiece, varying the string tension to create vibrato and other pitch variations. The string tension is balanced against a single, short helical compression spring, positioned under the arm pivot. Blues-rock guitar pioneer Lonnie Mack, who considered Travis one of his three most significant guitar inspirations, was known for using a Bigsby on his 1958 Gibson Flying V electric guitar. The Bigsby remains popular, especially on hollow-body guitars. It's available as a factory-fitted option on top-line models both hollow and solid-bodied from many makers, and as an aftermarket addition. It remains the only widely used design whose mechanism is entirely above the belly of the guitar body, making it particularly suitable for acoustic and semi-acoustic guitars. Fender designs After the Bigsby, the next major development was Leo Fender's synchronized tremolo, the device that introduced the term tremolo arm ( filed in 1954, issued in 1956). First released in 1954 on Fender's Stratocaster, the simple but effective design offers a greater range of pitch change than the Bigsby, and a better capability for up-bends. Fender wrongly labeled the arm as a "tremolo arm"