Respectful rebels: The Invergordon Mutiny and Granny's MI5 file
On the morning of Tuesday 15 September, 1931, the Cromarty Firth rang to cheers from the Royal Navy ships lying off Invergordon.
This wasn't an outbreak of patriotic fervour, but the sound of thousands of sailors coming out on strike - the Invergordon Mutiny had begun.
It's called a mutiny, but it's more accurate to call it an industrial dispute carried out by servicemen who were supposed to have left their civilian rights at the gang plank.
In 1931, the Great Depression was two years old and had eight yet to run. Britain's new National Government was making massive austerity-driven cuts to public sector pay.
Some of the worst hit of all were the older ratings of the Royal Navy. They faced a 25% pay cut at a time when they barely earned more than men on the dole.
Then the Admiralty made it worse. It botched breaking the bad news to the 12,000 men of the Atlantic Fleet, then at sea.
The orders were put in the post, which crawled to Invergordon more slowly than the warships steamed, and the men received the shocking news from the papers when they landed.
The cuts spelled ruin for them and their families. They had only one weapon - to strike - but that would be called mutiny, and mutiny could mean death.
But with no alternative, they went ahead. Planning their action in canteen meetings ashore, the men decided to strike when the largest force was scheduled to depart.
The crucial moment came at 8am that Tuesday, when four ships were to sail. But HMS Valiant, the first due to depart, wasn't getting up steam. Instead, after the familiar flag ceremony took place on deck, her men assembled on her fo'c's'le and they cheered and they cheered and the other striking ships answered back.
Although it's not known how many sailors were actively involved, it was enough: the strike was on.
According to historian Dr Tony Carew, this was no Soviet style workers' revolt, but "a curious blend of defiance and respectfulness".
Men avoided their officers so as not to disobey direct orders, and the officers didn't force things. But the government didn't see it that way.
As the mutiny stretched into its second day, it struck utter existential fear into the British establishment.
The Admiralty finally came up with a face saving solution. They ordered the ships to sail for home ports down south, promising to help hardship cases, but even though it ended the strike, it did nothing to damp down the terror which had seized the government - and crucially the security services.
They were convinced that communist agitators lay behind the mutiny and that they were plotting to strike again.
Paranoia now turned into dark farce. Naval intelligence sent agents to the ports, some posing as radical sailors, looking for agitators. Meanwhile the Communist Party, shocked that they'd missed the mutiny, sent its men to the Portsmouth bars also hunting for radical sailors. There were no radical sailors.
The hunters soon bumbled into each other. The secret agents sprang a trap on the Communists and charged them with incitement to mutiny.
One man, however, got away: Stephen Hutchings, a journalist for the Soviet photo agency TASS. More than 80 years later, his granddaughter Jacquie Montgomery knew Stephen had had to flee to the USSR, but what she didn't know was that her Scottish granny, Fiddy Hutchings, had an MI5 personal file several inches thick.
In it were passport photos, family letters (intercepted and microfilmed), and even an account of family history (compiled by the Perth police). The file was still growing as late as the 1950s, 20 years after Invergordon. It's a surprising way to get a detailed slice of family history.
On the 27 August 1932, Fiddy sailed from London to Leningrad, taking three of her children, Harriet, Cadie and Stephen. The family lived in one room with their father at a Moscow hotel.
Fiddy returned to the UK with her family in September 1933, leaving Stephen a fugitive in Russia. She was now faced with the challenges of being a single parent in harsh economic times.
A few years later, their young son died in an accident while his father was still in exile. But as the file reveals, this increasingly tragic family separation was unnecessary.
Husband, wife and children could have reunited long before if they had only known one vital but uncommunicated fact.
No-one from the authorities bothered to tell Stephen that from July 1933 they had decided that his prosecution in relation to the Invergordon Mutiny was now "undesirable". He could have come home to his family after all. Instead, he never saw them again before he died in Russia in 1937.
Stephen Hutchings was not the only scapegoat for the Invergordon Mutiny. Naval careers were destroyed.
Twenty four so-called ringleaders of the strike were unceremoniously kicked out of the Navy. A further 93 men were groundlessly discharged.
Some of these men, previously no radicals, were now destitute and turned to the Communist Party. One, Able Seaman Len Wincott, went to Russia as a hero of the mutiny (although he would later spend 11 years in a Stalinist Labour camp), but no Communism lay behind the mutiny.
Tony Carew found that all the efforts of the Communist Party to recruit serving sailors in the naval ports in the 1930s produced very little effect.
The institutional panic over the strike was based on nothing. The effects on families like the Hutchings were very real.
BBC Radio Scotland's programme on the Invergordon Mutiny, The Spirit of Invergordon, presented by Hamish MacDonald and telling the story of the mutiny, Hamish's own family and the Hutchings family, is broadcast at 13.30 on 21 December 2016.