Without knowing any context, it has to be a shield named for a connection either to a person with the last name Harlow-Greathead or one named for two people that share credit or connection to it for some reason. If someone who’s last name was Harlow and someone who’s last name was Greathead jointly discovered or published something important about this shield it could be named like that. Context would help a lot though. Ok I looked it up and this appears like it should be Barlow-Greathead Shield. I don’t know how the shield works in this case but it’s a device for digging tunnels. It seems Greathead came up with an improved design after Barlow and the Barlow-Greathead name given to the device shows both of their contributions. The Wikipedia article on it names it without Barlow’s name and claims Greathead’s design was significantly different from Barlow’s. I didn’t dig any further into it.

Inventions, discoveries, laws, and other things may be named after the person responsible. For example: --the Edison effect (discovered by Thomas Edison) --the Pribilof Islands (discovered by Gavriil Pribylov) --the Whipple procedure (developed by surgeon Allen Whipple) --the Diesel engine... etc. etc. When there are two people who should be credited, they are often named by combining two surnames with a hyphen: --the Smoot-Hawley tariff (developed by congressmen Reed Smoot and Willis Hawley) --the Clausius-Clapeyron equation (developed by scientists Rudolf Clausius and Benoît Paul Émile Clapeyron) --the Hertzsprung-Russell diagram (star classification system developed by Ejnar Hertzsprung and Henry Norris Russell) The grammar, I guess, is that a) a compound word is produced by joining two surnames; b) the surnames are proper nouns, but c) in English it is quite common to use nouns as adjectives. In particular, instead of using the strictly correct possessive form ("Hudson's Bay"), it is common to simply use the name as an adjective meaning "developed by" or "discovered by" ("Hudson Bay.")