North Korea detonates its biggest nuke yet; Army rapid-reaction brigade says it’s unready; ISIS fight gets new US commander; Spy satellites set to shrink; and just a bit more...

North Korea conducted its sixth nuclear test over the Labor Day weekend, extending its streak of being the only country to test nuclear weapons in the 21st century. How big was the bomb? “The explosion was so powerful that USGS recorded a second seismic event a few minutes later, which appears to have been a collapse inside the cavity created by the explosion,” @armscontrolwonk Jeffrey Lewis writes for Foreign Policy.

Need-to-know: “That’s an order of magnitude larger than anything North Korea has ever exploded before and about the same yield as modern U.S. thermonuclear warheads.”

U.S. officials are so far calling it an “advanced nuclear device.” That, Lewis writes, is “a bit of a hedge because they are still waiting to see if the test releases any radionuclides that might give a hint as to the composition of the bomb.”

The bottom line, according to The Diplomat’s Ankit Panda, writing in War on the Rocks: “for strategic deterrence purposes, [whether it was an actual staged, thermonuclear device — as North Korea claims] does not matter. All that matters is that the explosive yield is large enough to flatten cities and the device is ready for use in ballistic missiles. And given the magnitude of the seismic data, it seems clear North Korea unquestionably demonstrated that ability.”

Pyongyang also released photos purporting to show a thermonuclear device that can fit atop an ICBM. See those, via Max Fisher, here.

North Korea is “begging for war,” the U.S. Ambassador the UN, Nikki Haley, said Monday. "War is never something the Unites States wants -- we don't want it now," Haley said. "But our country's patience is not unlimited. We will defend our allies and our territory." More from CNN, here.

Extra listening: Dennis Wilder, “who served on President George W. Bush's National Security Council for East Asia and as deputy assistant director for East Asia at the CIA,” spoke with NPR’s Rachel Martin this morning about the slate of U.S. options with regard to North Korea now. He disagrees with Haley’s assessment (“begging for war”). That discussion runs about five minutes, and begins here.

Oh, and the North Koreans “went out of their way to taunt us about electromagnetic pulse (EMP) effects,” Lewis wrote, “I suppose because they think we’re worried about them.” (FWIW: he maintains fears over an EMP attack is a “laughable” position to take.)

One sober recommendation for the U.S. and its allies: “Reducing the risk of war — nuclear war — will require both sides to set up military-to-military channels to manage risk,” Panda writes, “and, above all, for the United States to stop doubting that North Korea indeed possesses the capabilities it has now dramatically demonstrated.” Worth the click, here.

From Defense One

The Clear Logic of the Latest North Korean Test // Joshua Pollack: Kim Jong Un has a predictable purpose and a plan.

As China Rises, the US Must Stop Taking Australia for Granted // Bradley A. Thayer and Michael Wesley: Canberra's and Washington's strategic preferences for confronting Beijing are diverging. Here's how to bring them back together.

Future Spy Satellites Just Got Exponentially Smaller // Patrick Tucker: By changing the way microchips measure light, researchers are shrinking the size of space-based telescopes.

Welcome to Tuesday’s edition of The D Brief by Ben Watson and Bradley Peniston. OTD1939: U.S. declares its neutrality in just-begun World War II. Have something you want to share? Email us at the-d-brief@defenseone.com. (And if you’re reading this on our website, consider subscribing. It’s free.)

The U.S.-led coalition fighting ISIS gets a new commander: Lt. Gen. Paul Funk II took command from Lt. Gen. Stephen Townsend today, CENTCOM announced this morning. Funk previously commanded the III Armored Corps, and Townsend commanded the XVIII Airborne Corps.
Along with the change of command, CENTCOM offered some stats on the ISIS war to date, including:

• Nearly 115,000 Iraqi Security Forces (ISF) and over 11,000 vetted-Syrian counter-ISIS forces have been trained and equipped by coalition forces;
• The coalition has "recaptured over 82,000 square kilometers of territory previously held by ISIS in Iraq and Syria;"
• Over 5.5 million men, women and children have been "set free" by the coalition across Iraq and Syria;
• And coalition jets have carried out more than "26,000 strikes against ISIS in support of partner forces in Iraq and Syria."

In Syria, pro-Assad forces have reportedly reached the eastern city of Deir ez-Zour, Syrian state media says this morning. The advance, AP reports, breaks a “nearly 3-year IS siege on government-held areas” around the eastern city.
Mapped: Areas of control inside Syria since March. Watch the further degradation of ISIS-held turf alongside the gains made by pro-Syrian forces in this visualization from Reuters, published this weekend.
For your eyes only: Russia shot a few more cruise missiles off in Syria on Monday. The stated targets: ISIS fighters near Deir ez-Zour. Video of that, here. Adds AP: “Tuesday’s firing of cruise missiles came a day after the Russian defense ministry said two Russian troops were killed in shelling in Syria’s east. The ministry’s statement quoted by Russian news agencies late on Monday said the two men died when a convoy escorting Russian cease-fire monitoring staff came under mortar fire outside the city of Deir el-Zour. The ministry said one man died on the spot and the other died later of his wounds in a hospital.”

A U.S. Army rapid-reaction force says it is ill-prepared to counter Russia or its proxies in Eastern Europe. “The Italy-based 173rd Airborne Brigade, a bulwark of the NATO alliance that has spent much of the past decade and a half rotating in and out of Iraq and Afghanistan, lacks ‘essential capabilities needed to accomplish its mission effectively and with decisive speed,’” according the brigade’s own self-analysis, a copy of which was obtained by Politico. The eye-opener was apparently an exercise with Ukrainian troops who described their brutal combat with Russian-backed separatists armed with cheap drones, electronic warfare tools, and state-of-the-art antitank missiles. Read on, here.
ICYMI: It’s hardly news that new methods of warfare have been making their debut in the disputed east of Ukraine. Get all of Defense One’s coverage in “Lessons from the Russian Front” ebook, here.

U.S. states’ election boards short of cash to ward off foreign attackers. Speaking of Russia and new ways of war, this deep dive from Politico shows just how lacking are funding, efforts, and federal urgency — one year after a spate of intrusions and one year before a new set of national elections are sure to draw more sophisticated and emboldened hackers.
“States ought to get their own money up,” said Sen. Richard Shelby, R-Ala., who chairs the Senate Committee on Rules and Administration, which oversees federal elections. “We’re borrowing money. We got a big debt limit coming up.” Read on, here.

Lastly today: Hollywood fumbles in its portrayals of the realities of war, The New York Times reports reviewing the fall TV line-up this year. Some of the shows on the docket: “Valor,” “SEAL Team,” “The Brave.”
Writes the Times: “The military may be having a TV moment, but… these shows assume that the public doesn’t want a deep engagement. Instead, they present combat as a quick-hit operation. War may be hell, but this fall it’s just another action-drama genre… There are about 1.3 million Americans on active duty, and their service is vast and varied. But you wouldn’t know it to watch these shows."
One break from this deluge of action: Ken Burns and Lynn Novick’s “wrenching 18-hour documentary” PBS series, “The Vietnam War,” coming in about two weeks.