There are various kinds of abbreviation. It Yourself, DSS for Department of Social Security, gbh for grievous bodily harm, JCB for a machine invented by Joseph Cyril Bamford. Some abbreviations are the first part of a longer word and are pronounced as words, not said as a sequence of letters of the alphabet. Other abbreviations made by cutting off the end of the word are not used in speech, for example adv for adverb and cont for continued. If these need to be read aloud, they are read as the unabbreviated full forms.
Some words lose bits in the middle.
Dr , ft , Mr , and Mrs are other examples. These are read aloud as their unabbreviated full forms. A few words lop off the first part, for example bus and plane , though these are now so well established that they are really no longer thought of as reduced forms, but as words in their own right. There is a significant proportion of abbreviations which it is possible for an English speaker to pronounce as words rather than as sequences of letters of the alphabet. A few abbreviations are pronounced both ways, VAT being the prime example.