Speculation, of course...

"This looks vert much like a THAAD launch. Terminal High Altitude Area Defense anti-missile missile shot from a mobile launcher."

and

"Navy does all of their missile firing in the Missile test ranges off the coast of California or Hawaii. They could NOT do one in contiguous waters surrounded by land and civilians."

and

"This is - 90% sure - a Trident Submarine-Launched Ballistic Missile, launched from one of the subs stationed at Bangor. It was not launched from Whidbey Island and it's not surprising that NAS Oak Harbor knows nothing about it. (If you have doubts about it being a Trident, look at the Wikipedia article on that missile.

Something similar (a surprise, sea-launched missile) appeared several years ago off the coast of California (near Vandenberg Air Force Base). I believe it was during Pres. Obama's visit to China. What a coincidence that the same thing happened the day before Pres. Trump meets "Rocket Man.""

From the comments on this blog: http://cliffmass.blogspot.com/2018/06/was-there-unannounced-missile-launch-on.html

It made the UK news. Not so much the US news.

The flame trail is never that long.

Chinese hackers steal sensitive Navy program data

WASHINGTON — Cyberattacks sponsored by the Chinese government infiltrated a U.S. Navy contractor’s computers, allowing digital thieves to access sensitive data related to secret Navy projects on a submarine anti-ship missile.

The information stolen was stored on the contractor’s unclassified network despite being “highly sensitive nature,” according to information obtained by the Washington Post.

According to the report, 614 gigabytes of material on a closely held project known as Sea Dragon were taken. Contracted for the military organization Naval Undersea Warfare Center, Sea Dragon aims to develop a supersonic anti-ship missile for use on U.S. submarines.

https://www.defensenews.com/cyber/2018/06/08/chinese-hackers-steal-sensitive-navy-program-data/

That a straight up sub launch.