GB190926240A, Hughes, Howard Robard, "Improvements in Drill Heads", issued 1910-02-24
US1010406A, Hughes, Howard Robard, "Roller-drill", issued 1911-11-28
AT52632B, Hughes, Howard Robard, "Rollen-Drehbohrer", issued 1912-03-11
AT65852B, Hughes, Howard Robard, "Erweiterungsrollendrehbohrer", issued 1914-07-25
US1119163A, Hughes, Howard Robard, "Roller boring-drill", issued 1914-12-01
GB191312560A, Hughes, Howard Robard, "Improvements in Roller Boring Drills", issued 1914-05-28
AT69262B, Hughes, Howard Robard, "Rollendrehbohrer", issued 1915-07-10
GB101162A, Hughes, Howard Robard, "Improved Method of Sapping or Destroying Military Trenches Blasting and the like", issued 1917-01-11
GB102920A, Hughes, Howard Robard, "Improvements in or relating to Drilling Machines", issued 1917-01-18
GB106264A, Hughes, Howard Robard, "Improvements in the Method of and Apparatus for Forming and Enlarging Bore Holes", issued 1917-07-12
FR492296A, Hughes, Howard Robard, "Perfectionnements apportés à la construction des machines perforatrices utilisées pour le forage des trous horizontaux", issued 1919-07-03
FR492851A, Hughes, Howard Robard, "Perfectionnements apportés au procédé et à l'appareil permettant de percer et d'élargir les trous de forage", issued 1919-07-24
