FamousHolst chordsStar Wars, 1977 · John Williams
Two chords at once: D♭ major over a bare fifth on C
Right after the opening crawl, as the Star Destroyer chases the rebel ship (about 0:02:10; 'Main Title/Rebel Blockade Runner' bars 44-50); again at the climax of the Battle of Yavin, and in The Rise of Skywalker
A D♭ major chord slammed down on top of a low C and G, so two harmonies a half step apart sound at once. It is the pounding brass that greets the Star Destroyer just after the Star Wars opening crawl, and Williams himself called these the Holst chords because they echo 'Mars' from Holst's The Planets. The half-step rubs, C against D♭ and G against A♭, are what make it sound like a war machine.
Also called Holst, Martial Chords (Lehman's catalogue name), the Mars chord
Sources: Frank Lehman, Complete Catalogue of the Musical Themes of Star Wars (updated 19 June 2023), Incidental Motifs no. 3 'Martial Chords' · Pearson Edexcel GCSE Music set work guide: John Williams, 'Main Title/Rebel Blockade Runner' (2016) · Aaron Krerowicz, 'Imperial Attack vs. "Mars" from The Planets' (2013) · Scott Murphy, 'Non-Holst in the Score to Star Wars', SMT Discuss (2015)