Has the downing of a spy airplane ever been a justifying ground for waging war or causing an escalation that might lead to war?

Question

Both the cause of the collision and the assignment of blame were disputed. The U.S. government stated that the Chinese jet bumped the wing of the larger, slower, and less maneuverable EP-3. After returning to U.S. soil, the pilot of the EP-3, Lt. Shane Osborn, was allowed to make a brief statement in which he said that the EP-3 was on autopilot and in straight-and-level flight at the time of the collision. He stated that he was just "guarding the autopilot" in his interview with Frontline.[19] The U.S. released video footage from previous missions which revealed that American reconnaissance crews had previously been intercepted by the same aircraft.[20]

Based on the account of Wang Wei's wingman, the Chinese government stated that the American aircraft "veered at a wide angle towards the Chinese", in the process ramming the J-8. This claim cannot be verified since the Chinese government did not release data from the flight recorders of either aircraft, both of which are in its possession.[21][22][23][24][25]

https://en.wikipedia.org/wiki/Hainan_Island_incident

Has the downing of a spy airplane ever been a justifying ground for waging war or causing an escalation that might lead to war? If a country sends a spy airplane and the airplane gets shot down within the territory of the nation being spied upon, can the country that lost the airplane use this as an escalation towards war or even declare war outright? If this can't be answered, then was there a precedent for doing so before? Because in this case, the U.S. said it was sorry and tried to defuse the tensions between China and the U.S.

Answer 1

This kind of thing really depends on the country being spied on. Are they looking for an excuse to go to war? If so then sure, they'd absolutely cite this as a casus belli. Otherwise they won't (but of course, because people hate being spied on, tensions will escalate - this will happen even if it the spying is between friendly countries).

Historical parallel: in 1960, the USA flew a U2 spy plane over the USSR. It was shot down and the pilot captured alive. The USSR could have gone to war with the US over the incident, but if that gives you pause (it should), it also gave USSR premier Khrushchev pause. Khrushchev did react - he laid a diplomatic trap and embarrassed US president Eisenhower, the Four Power Paris Summit was ruined, he brought about a UN resolution that would have condemned "US aggression" - but he did not go to war. Who wants a war between nuclear-armed states which neither would win anyway?

Comparatively if Poland had flown a spy plane over Nazi Germany in 1939, and it was shot down, you can be sure Germany would go to war, because they were already looking for a casus belli (c.f. Gleiwitz incident).

Answer 2

First, this is a poor motivating example as the US plane was well outside Chinese airspace (per comments) when the collision occurred, although it did make forced landing in China thereafter. As for what "sorry" meant:

The United States stated that it was "not a letter of apology", as some state-owned Chinese media outlets characterized it at the time, but "an expression of regret and sorrow". China had originally asked for an apology, but the U.S. explained, "We did not do anything wrong, and therefore it was not possible to apologize".

And then China released the crew.

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As for the actual Q, wars or escalation is often undeclared in modern times, but the shootdown (in June 2012) by Syria of an unarmed Turkish F-4 described as an "RF-4E Phantom II reconnaissance jet", while officially was discounted by both sides, was the precursor of a series of cross-border artillery exchanges in October, as well as an official parliamentary authorization for the Turkish military to enter "foreign countries", understood to refer to cross-border raids into Syria.

The motion read that it was “to send the Turkish Armed Forces [TSK] to foreign countries and giving it [the TSK] that mandate, according to principle causes that will be designated by the government,” raising questions about the definition of “foreign countries,” although the remainder of the motion clearly designated Syria as a target for possible cross-border operations. [...]

“This should not be interpreted as declaration of war, it is designed as a precaution,” [Turkish defense minister] Canikli said, adding that Turkey perceives the mortar fire that struck the border town of Akçakale on Oct.3 as having been “deliberate.”

I'm not going to do any statistics on this, but the list of air incidents (involving recon planes) that didn't lead to a military escalation is probably much longer. E.g., in roughly in the same area as in your example, North Korea intentionally shot down a US spy plane in 1969. Although the US considered some retaliatory moves, not much came of that. (And yeah, as drones took over the job, the number of instances were they downed by collison or otherwise but not resulting in an escalation, probably also increased. FWTW, it's been recently revealed that a Russian pilot, upon misunderstanding a command, fired one or two missiles on an manned UK reconnaissance plane over the Black Sea, but luckily neither missile hit the target [the motor of one failed to ignite apparently, the other failed to lock on]. The UK accepted the official Russian line that it had been a "technical malfunction".)

BTW, while [more or less] everyone knows about the U-2 incidents (plural, because another was downed over Cuba during the missile crisis, and several over China--albeit the latter were flown by Taiwanese pilots), cold war incidents were probably more common than acknowledged [till much later], e.g. the Soviet shootdown of a Swedish DC-3. The Swedish side denied the plane was spying (until they admitted much later.) The Soviet side denied they shot it down, until after the fall of the USSR.