A Very Brief History of Men’s Swimwear.

[Torchwatch]

There was a problem in church choirs in England some years ago, because they couldn't recruit enough boy trebles they started letting girls into the choirs. Girl's voices don't break so the girls could continue in the choir beyond the age of 12.
11 year old boys reaching their peak potential as solo treble singers were being dominated by much older girls wanting the solo parts for themselves. The boys left and the choirs went all girl.

Up to the age of 11 boys having women swimming teachers is not an issue, they are used to women primary school teachers and swimming is just another learning experience. After the age of 11 boys need male role models and sports coaches can fill these roles, otherwise the boys will leave.
My own school swimming teacher (at the old municipal pool) Mrs Fox was evil, she set out to make children more afraid of her than of the water, fortunately I could already swim.

A competent male swimming coach being offered a squad that trains at 05-30 hrs would probably find a better offer elsewhere, knowing that this squad has been traditionally bottom of the league would make him avoid that school and keep his own kids well away. The school needs to find a better slot perhaps at another pool, 05-30 hrs training sessions are for elite squads only. getting a better slot will get you a better coach and a better squad.

[midlifeswimmer]

The 1970's Speedo 100% nylon suits came in both 4 and 3 inch sides. The 4 inch side ones had five-digit model numbers in the 70000 series, the 3 inch side ones were in the 72000 series. 70001 and 72001 were the solid color model. Then there were various sewn panel variations.

[Minimalist75]

The Speedo Solar must have arrived later.
It had a 1" side seam.
Rumor had it that one of the advantages of it was that you could tan in it and there was little chance of any of the untanned area showing when wearing a 2" competition brief.

[Torchwatch]

Here in England we were never offered the Speedo Solar or the Speedo Thong, but before the introduction of Lycra we had a choice of 3" and 2" side designs in nylon.
Getting 3" black nylon Speedos was an adventure and then to discover they do them in 2" wow!

[Minimalist75]

In the US, Solars were easy to find, thongs less so.