The VF-1 Valkyrie series were the first Human designed and built series of Veritech fighter. Each Valkyrie had three modes, Battloid, Guardian and Fighter, and were the most versatile mecha used by humanity during the First Robotech War. The Valkyries were built using the knowledge gleaned of robotechnology thanks to the arrival of the SDF-1 on Earth.
Dubbed Project Valkyrie, the creation of the first transformable fighter began in 2006 on Macmartin Island, just off Macross Island. Doctor Emil Lang led the team in designing and constructing the Valkyrie, Lieutenant Roy Fokker was the chief test pilot and Lieutenant Colonel T. R. Edwards commanded the entire project. 
Following an attack on the prototype by Anti-Unification League fighters that saw Fokker crash the prototype, it was briefly shelved for the Project Excalibur. (Comic: "Robotech: From the Stars 5: The Gathering Storm") The project was restarted after Fokker successful used the prototype to kill the hijackers of Armor-1 and destroy a reflex missile that was launched at Macross Island. 
First Robotech War
The United Earth military was able to keep the Valkyrie's transformable capability a secret, even from the civilian inhabitants of Macross Island were a large number of Valkyries were based, until 2009 when the Zentraedi attacked Earth and multiple Valkyrie squadrons were deployed to fight off the invaders. 
The VF-1A Valkyrie was the standard model of Valkyrie assigned to new recruits used by the Robotech Defense Force during the First Robotech War and came in a light brown colour scheme. Young ace pilots were in VF-1As had a mostly-white colour scheme. In 2014, the VF-1R model started to replace the VF-1A. (Robotech Infopedia)
The VF-1R Valkyrie was designed as a stop-gap fighter to bridge the gap while the next-generation Advanced Veritech Fighter was in development. The older VF-1A and VF-1J models were gradually replaced by the VF-1R, which offered better survivability.
The VF-1R featured three cannons mounted on the head of the Veritech. Two of the cannons are like those on the the VF-1J models. The third cannon is a pulse autocannon operated independently of the pilot and was used for point defense to shoot down incoming missiles and other ordinance, allowing the pilot to concentrate on other tasks. 
The VF-1S Valkyrie was one of the rarest models of the VF-1. The model was specifically designed for commanding officers of Veritech squadrons. Only a dozen had been built when the First Robotech War began. 
The most famous VF-1S was the prototype, the VF-X-1, otherwise known as Skull-One. Skull-One survived the entire First Robotech War and was piloted by two of the most celebrated pilots of that conflict, Roy Fokker and Rick Hunter. It was eventually dismantled in 2015. (Comic: "Robotech: From the Stars 0: Promises")
The VEF-1 was a version with an attached radome, used for electronic warfare and AWACS duties. It did not carry the gun pod.
Super Valkyrie had the MVAS-1 FASTpack armor and booster attachments. It added a number of mini-missiles to the Veritech's armaments and was mainly used in spaceborne operations.
The Armored Valkyrie had the GPB-1S armor system. It was limited to battloid mode. Rick Hunter once piloted his VF-1J with the armor to investigate a Cyclops recon vessel, although he jettisoned the armor.
Jotun Armored Valkyrie
The armored MVAS-3 FASTPack Seamaster Valkyrie was a stopgap armor system to allow the fighter to operate under water while dedicated platforms were under development.