Yep, that is definitely a nice old Underwood--but it's definitely not the bog standard 1920s Underwood 5 that you can still find laying around today.
The multiple fraction keys, lack of a 0/) key (using capital O for 0), British £ symbol, deeply wrinkled paintwork suggesting a refinishing in the then-fashionable crinkle finish, and fascinating sans-serif celluloid keytops (as opposed to the glass-topped paper keys it would have had originally) tell me that this was a model probably exported to British-controlled territories and rebuilt in the 1930s-1940s.
Why crinkly paint and fun keys?
Why not? The belief was back then that, under the harsh glare of overhead incandescent lighting, high-gloss paintwork would cause eyestrains. (Remember this is back when office workers wore green eyeshades.) And the delightful Art Deco keytops are in line with a 1930s-'40s rebuild, as the original Underwood keys, paper under glass, were usually very dated-looking even in the '20s. (The most up-to-date 1920s American typewriter, IMHO, was the Remington.)
42 keys printing 84 characters makes this an Underwood No. 5, as opposed to the No. 4 (which is less common and had fewer keys.) But it is pleasingly outfitted with a few variations.
The back spacer and bichrome selector (visible on front right of machine--red and blue buttons) were introduced in May 1909, and the early style shift lock lever was replaced in February 1915. Your Underwood is probably going to have a serial number range between #247001 and #750,000.
Considering serial numbers on the Underwood No. 5 stopped at 3,885,000(!) there are plenty of them out and around for typewriter collectors, but most of them won't be so nicely outfitted.
Here is my Underwood 5 that I just got the escapement for--I was wrong, it is a 1927 version. This was rebuilt as a "Master Grade Underwood" some time in the early 1930s, but was not customized much--about the only cosmetic change really was losing the UNDERWOOD brand on the front plate. Seems to work in a lot of places, but I'm ludicrously picky about typewriters because I use them a lot. This one is currently disassembled but it's got to get the new escapement anyway, be de-rusted, probably get some fresh rollers.
I have a 1929 Underwood 5 that was found in un-rebuilt condition, which is neat because it was wearing original factory paint. It was basically scrap iron & missing a couple parts.
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Yep--Same typewriter but all fixed up and in service (after six months I'd rather not repeat.) I used black stove paint to do the bodywork, as it was both durable and glossy. The added pinstriping is closer to a 1915-1920 model, but I wanted to add the gold-and-blue striping because it came along with the decal kit I got and I wanted to make this look very pretty. I would have liked to gone fully original but decided that the rust and tarnishing were all in the past for it, and it could have some good new history in the form of cool stripes.
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Both of these are not as special as your early 1909-1916 Underwood--these are just regular old 1920s models--but again, never pay full price for second hand goods because you're going to have to end up fixing it if you want something that works.