Orthochromatic

Us youngsters do a quick check on the web  Of course this doesn't tell you what it's good for and anything about actually using it.

Orthochromatic photography refers to a photographic emulsion that is sensitive to only blue and green light, and thus can be processed with a red safelight. Using it, blue objects appear lighter and red ones darker because of increased blue sensitivity. Standard panchromatic film can be used with a Cyan-lens-filter (devoid of red light) to produce similar effect.

Orthochromatic films were first produced by Hermann Wilhelm Vogel in 1873 by adding small amounts of certain aniline based dyes to photographic emulsions which had hitherto been sensitive to blue light only, work that was extended by others including J. M. Eder, who introduced the use of the red dye erythrosine in 1884.[1]

It is not so much a matter of what it is/was good as much as that was the only film available for quite some time.  This is why many old photos have basically pure white skys.  The orthochromatic films were over sensitive to blue and skys were pretty much always over exposed if the subject was properly exposed.  Many photographer kept negatives with properly exposed skys and "dropped" those skys into their other photographs.  Of course this was loooooong before Photoshop!

Ed