First CO then UA has been sending 737's to Hawaii for years so I shouldn't be surprised but it still seems like a lot of water to cross, even though distance wise it's shorter than some west coast cities to Hawaiian destinations. The 737 MAX will be operating the seasonal EWR to Azores flight.
In a world of large 757s, 767s and 787s, this flight is the only one to be operated by a 737 MAX. In fact, it’s the first time United — or any U.S. carrier — is scheduling the workhorse 737 to fly transatlantically.
However, a flight from the U.S. to the Azores spans only about 2,576 miles (and takes 5 hours and 45 minutes), which is shorter than some of United’s West Coast-Hawaii flights likewise operated by 737s.
https://thepointsguy.com/news/united-737-max-azores-ponta-delgada/As the article states at the end, if this works out, how long will it be before some secondary markets in Europe might see UA TATL service?
What's the point of an open door policy if inside the open door sits a closed mind?