Since the solemn papal Mass was an incredibly complex ritual involving a very large number of people holding offices at the Curia and the papal court, including highranking prelates, it was only celebrated on rare occasions (for a brief description, see here). An alternative - although an extraordinary one - was the public celebration of a Papal Low Mass. At a Papal Low Mass (which was usually celebrated at a portable altar set up in one of the rooms of the Apostolic Palace and is distinct from the private Mass the Pope said in his private chapel), the Pope is assisted by two bishops and four papal Masters of Ceremonies. Chamberlains (cubicularii) served as torchbearers. The pontifical canon was used, as was the bugia.
Here is a video of such a Mass. The Mass was celebrated on 14 May 1942, the Feast of the Ascension, and the occasion was the Silver Jubilee of the Pontiff's episcopal consecration (you can find the text of the papal sermon in AAS 34 (1942), 167).
Video source: http://te-igitur.blogspot.com/
