As Historical Sources
Letters are useful as historical sources because:
they provide valuable information about the family, work and leisure experiences of people from all parts of the Navy.
they are one of the few historical sources, along with diaries and autobiographies, in which we can learn of the direct experiences of individuals.
Letters convey directly the experiences of sailors living through particular events They can be used as primary sources to describe a sailor's personal, working and leisure experiences. Letters may provide some factual information, but perhaps more importantly, they convey an individual's interpretation of events. When writing the letter, the author reveals, wittingly or unwittingly, their own attitudes values and beliefs.
Letters usually deal with events and experiences which have occurred in the last few days. In this way they have an advantage over autobiographies which are often written a long time after events.
However there are things to be aware of when using letters:
One consideration when reading letters is that most people wish to show themselves to the best possible light, they may either consciously or unconsciously interpret events to their advantage. Similarly you should be aware of bias within the source.
Letters are personal accounts - they refer to a particular person, particular ship or particular event, because of this care should be taken if generalising from them.
One of the more frustrating aspects of using letters as sources is that they do not always discuss the subjects in which you as the researcher are particularly interested.
See original letters and read the transcripts.