First usage of "get a handle on it"

Solution 1:

Under its entry for handle, the OED defines to get a handle on, as ‘to gain control over . . . to acquire the means of understanding or of forming an opinion about’ and the earliest citation in support is as late as 1972 from the ‘New Yorker’:

Scribner . . . said to me, ‘I don't think people have any idea of how tough it is for anyone in this job to get a handle on anything.’

However, under the entry for get, there is this citation from Charles Kingsley’s ‘Hereward’, published in 1865:

Driving them mad and desperate just that you may get a handle against them.

That doesn’t seem to have quite the same meaning as the ‘New Yorker’ citation, but if you’re looking for first use . . .

Solution 2:

An instance appears in a 1902 college magazine, found among 1500-1978 links at ngrams for get a handle on it,get a handle. Obviously it's a phrase not often found in books of that vintage, but ngrams says nothing about its frequency in spoken language.

A 1938 magazine article apparently uses the phrase too.

Solution 3:

Found this late 19th century use of the phrase that I think matches its more contemporary use. This is from an 1874 issue of The Atlantic Monthly: