In a little-noticed but significant move by the Trump administration, the United States has begun construction on its first military base within Israel.

The permanent facility flying the U.S. flag will be independently operated by American troops on the IDF Air Defense School grounds in southern Israel’s Negev Desert near Beersheba.  Its mission was described as defending against rocket and missile attacks.

But it’s also both a symbolic gesture of the deep political and defense solidarity that both countries’ leaders have stressed and a substantive one, since it places an unknown number of American military members on the ground where hostile fire has fallen. Both Trump and Prime Minister Benjamin Netanyahu have vowed that bilateral relations are now the closest in history.

Groundbreaking for the isolated, new U.S. base was first reported earlier this fall by Defense News, but attracted little immediate attention.

Speaking at the modest ceremonies, U.S. officers enigmatically called the facility Site 883 Life Support Area. “This life support area represents the first ever stationing of a U.S. Army unit on Israeli soil,” said Maj. Gen. John Gronski.

He added:

The U.S. and Israel have long planned together, exercised together, trained together. And now, with the opening of this site, these crucial interactions will occur every day. We’ll have Israeli airmen, U.S. soldiers living and working side by side.

Israel has purchased and already independently operates the U.S. Iron Dome missile system which has been effective against rocket attacks from Israel’s neighbors. Defense News also reported the existence of a sophisticated U.S. radar facility within Israel that helps track incoming rockets or missiles.

The new base, which will contain housing, recreational and other installations for American personnel, will also have anti-missile armaments.

It’s a concrete sign of the increased seriousness the Trump administration is directing toward Iran’s ongoing ballistic missile development program. That program was not included in the nuclear agreement the Obama administration and allies negotiated with Iran, an agreement severely criticized by both candidate and President Trump.

Officials were vague about the scale of the new U.S. facility, referring only to dozens of Americans. But Israel’s air defense commander, Brig. Gen. Zvika Haimovich, stressed the new base’s different mission. “The purpose of their presence is not for training or for exercises,” said the general, “but rather as part of a joint Israeli and American effort to sustain and enhance our defensive capabilities.”

Haimovich also said the Americans’ presence “would not hamper the IDF‘s ability to act independently against any threat to the security of the State of Israel.”

Which could seem to suggest the unusual arrangement on foreign soil that the Americans would also be operating independently.

Separately, President Trump has revived the idea of a U.S. anti-missile system based in Poland, anticipating possible Iranian missiles. The system’s presence was negotiated by the last Bush administration but peremptorily abandoned by Obama in 2009 as a sop to Russian objections.