What is the significance of this roof structure which looks like a soldier’s helmet? Does it have any connection to the organisation known as the MOTHS – Memorable Order of Tin Hats? This Promenade Dome is commonly known as “The Tin Hat” from its resemblance to a First World War helmet but could not have had any connection to the Moth order as it was only founded in 1927 whereas this structure was built in 1923.
Main picture: Humewood promenade in 1909

During this era, this promenade, on which this Promenade Dome was located, was officially known as the “Princess Promenade”. During November 1923, the Governor-General, Prince Arthur of Connaught, and Princess Arthur paid a short farewell visit to Port Elizabeth. On the 6th November, Prince Arthur opened the Campanile and laid the foundation stone of the first Scouts’ Hall, at North End, presented by Mrs. A.M. Gibaud.

While the Prince was busy with these two official openings, it was Princess Alexandra who opened the “Princess Promenade” at Humewood. The promenade was built in sections over several years. The official opening took place under the Promenade Dome, designed by the Assistant City Engineer, J.J. Burt. Commonly known as the “Tin Hat” from its resemblance to a First World War helmet, there was a bronze plate, the work of J. Gardner, to commemorate the occasion, but like many such valuable pieces of bronze, it soon disappeared probably being sold to a scrap merchant.


Source
Port Elizabeth: A Social Chronicle to the end of 1945 by Margaret Harradine (2004, Historical Society of Port Elizabeth, Port Elizabeth)
I would like to make a slight correction to the above explanation of the acronym MOTH. It does not stand for “Member of the Order of Tin Hats”, but rather “Memorable Order of Tin Hats”, as confirmed by Wikipedia, or else “Memorable Order of the Tin Hat”, as insisted upon by Dam Buster Leonard Cheshire, while I listened to him on 4 and 5 November 1977, as he fished on the beach at Bloubergstrand, with his friend, my Grandfather, Group Captain Horace Weldon. It was my job to bait the hooks.