'Great Monster Duel: Gamera vs. Barugon') is a 1966 Japanese kaiju film directed by Shigeo Tanaka, with special effects by Noriaki Yuasa and Kazufumi Fujii.

In the film, Gamera returns to Earth to battle a reptilian monster born out of an opal brought to Japan by greedy entrepreneurs.

Due to the success of Gamera, the Giant Monster, studio president Masaichi Nagata pushed a sequel into production.

Yunosaburo Saito was commissioned to write a story outline, which featured Gamera battling alien ice giants.

Gamera vs. Barugon was theatrically released in Japan on April 17, 1966, on a double bill with Daimajin and underperformed at the Japanese box office.

Ichiro, a World War II veteran, sends Kawajiri, Onodera, and his brother Keisuke, to the island of New Guinea to retrieve an opal he once found and hid in a cave.

Despite warnings from the local villagers, the trio find and locate the opal, but Kawajiri dies from a fatal scorpion sting.

While debating how to recover the opal, which he still believes to be aboard the sunken ship, Onodera inadvertently blurts out that he killed his two companions and then murders both Ichiro and his wife to cover up his crime.

Keisuke and Karen suggest a plan to the defense ministry by using a huge diamond to lure Barugon into a lake to drown.

Another attempt by irradiating the diamond with additional infrared radiation almost succeeds, until Onodera interferes and steals the gem.

[7] Yuasa recalled that Daiei wanted to target the film to an adult audience, stating, "I thought that mixing melodrama and monsters was difficult to do.

[4] Hongo felt "stuck" with performing in the film and initially attempted to drop out by faking an illness, which caused production to delay for a month.

[9] Hongo did not read the script after receiving it, believing that little acting was involved due to Yuasa telling him where the monsters would be placed.

[16] Takahashi was inspired by the Jötnar from Norse mythology and the snow giants from The Conquest of the Pole, however, the ice creatures were redeveloped into Barugon.

[21] The script opened with Keisuke Hirata flying a Cessna with his instructor over Osaka, only to lose control due to radio interference.

I always had to be extremely conscious wondering the wires would be visible on-screen or not and I even had to be concerned with such details as to the position of movement of Barugon's legs when he leapt into the air.

[34] Yonesaburo Tsukiji, the effects director of the previous film, did not return due to leaving Daiei to form his own company.

[40] After returning to Tokyo, Takayama worked in Equis’ workshop to build full scale suits and miniatures of both monsters and a gimmick version of Barugon capable of spraying mist from its tongue.

"[48] The shrieking sounds for the cave bats were originally produced for the rat creatures for the unproduced film Nezura.

The international dub by Axis features the voices of Barry Haigh, Warren Rooke, and Ted Thomas.

AIP–TV retitled the film War of the Monsters and removed 12 minutes of footage to fit commercials into a two-hour timeslot and prevent children from growing restless.

"[59] Christopher Stewardson from Our Culture awarded the film three stars out of five, praising the monster scenes and human drama, but criticized the pacing and military meetings, stating, "Gamera vs. Barugon presents an entertaining story with interesting themes.

"[60] James McCormick from Criterion Cast praised the film's miniatures, cinematography, and Kōji Fujiyama's portrayal of Onodera.

[61] Kurt Dahlke from DVDTalk criticized the film's lack of monster battles but praised other elements, stating, "there are still plenty of sweet moments (including a giant tongue lashing) and stomped buildings, plus a generally serious tone, that marks this as a high-point in the Gamera franchise.

"[62] In the late 1980s, the export English version by Axis International debuted on VHS in the United States via the Sandy Frank Film Syndication and Celebrity Home Video.

[55] In 2003, a public domain, pan and scan version of the AIP-TV English dub was released on DVD by Alpha Video.

Factory included the Mystery Science Theater 3000 episode featuring the Sandy Frank version of the film on the MST3K vs. Gamera DVD collection.

[64] In 2014, the Japanese version was released on Blu-ray and DVD by Mill Creek Entertainment, packaged with other Gamera titles.