On 5th December 1940, the British India Steam Navigation Co. Ltd.'s SS Gairsoppa left from the port of Calcutta, India to sail toward Britain. The cargo ship was carrying important war supplies including 2,817 Bombay Mint silver bars, tea and Royal Mail letters. On 16 February, just as the ship was nearing the end of its journey, a German U-boat torpedoed it and the ship sunk just off the coast of Ireland. The Gairsoppa went down in just five and a half minutes and remained at the bottom of the sea bed for the next 73 years.
At a depth of 4,700 metres, a cache of 700 letters, representing the largest collection ever found at sea, remained preserved until an expedition organised by the American company Odyssey
Marine Exploration began the salvage operations to bring the content of the ship back to land. The shipwreck revealed hundreds of letters never delivered to their destinations.
In 2017, the British Postal Museum and Archive (now Postal Museum) was approached to explore a possible interest in acquiring the collection of letters and other paper items. The organisation was at a crucial stage in its development as it was going from being an archive and a museum collection without a permanent home to become a new museum and attraction including the Postal Museum and Mail Rail. The historical value of the collection was immediately apparent, and the acquisition was agreed after fundraising secured the necessary funds to complete the operation. The collection will be used in an exhibition that will tell the story of this amazing find, how these objects survived and most importantly the stories behind some of these letters.

Conservation
We were informed that after the salvage operations, the collection had been transported to Scotland to an archaeological conservation facility to receive initial treatment.
The collection of letters arrived in the conservation studio stored in boxes, arranged in folders, divided into batches contained within polyester sleeves. The identification numbers were the ones assigned by the archaeological conservation studio that had first worked on the letters, prior to acquisition by the Postal Museum. The first task, after visual examination, was to decide together with curators and the Head of Collections which numbering system to adopt to catalogue the collection. Given the limited time we had before conservation work had to begin and be ready in the for the exhibition opening, it was decided to keep the numbering system used by the Scotland's conservators and thus keeping also the single batches in the same order as they arrived. Digitising the whole collection was desirable and doing so both before and after conservation will help keeping high quality accurate records of the collection. Fortunately, the Postal Museum has an in-house digitisation studio, so this was easily achieved.
Communication with the conservation studio that first worked on the items was vital to established previous interventions and to be aware of any potential issues with the collection.
Although the collection had survived remarkably well, given it had been at the bottom of the sea for over 70 years, unsurprisingly the letters were still very fragile and to be safely exhibited the main conservation issues had to be addressed. From handling the letters, it was obvious that the paper had lost all internal size resulting in a feathery absorbent texture very prone to breakage. Brown staining, due to proximity with metal components was evident on almost all items. Some photographs had survived well but most of them were nearly illegible and in some cases image transfer to other items had occurred making the identification of the photo difficult.
The other issue was that the fragmentary state of most of the items required a jigsaw-puzzle approach as in the case of letters of several pages that although luckily kept in the same polyester sleeve needed to be re-assembled before repair could take place. With ink almost completely faded in some sections, assemblage of these letters required a concerted effort with curators and a good eye for old fashion handwriting
As it was immediately clear that we could not conserve all of the items in time for the opening of the exhibition, the first step involved the identification of the items to select for display. The criteria had to take into consideration both the physical state of the items and the relevance to the story that curators wanted to present. Working with the Postal Museum exhibition officer and the head of collections, a first selection was presented to the studio and from this initial pool the final items were decided.
To keep the workflow as fluid as possible, a selection of items was sent to digitisation while others that had already been digitised received treatment. The main aim in treating the objects was stabilisation; we were not looking at 'beautifying' these items especially given their history, but rather to prevent them from receiving further damage and be safely exhibited. Paradoxically, in some instance letters were immersed in water as floating allowed sheets to be safely separated compared to doing it mechanically. Washing was done only when necessary to remove larger debris and primarily by floating.
When first examined, some of the stains on the letters had the appearance of mould. Multi-coloured patches radiating from a darker central point in a circular fashion could have been caused by mould spores, but we did not possess the capabilities to identify this with certainty, given that at the time of receiving the collection we were in the process of moving to the Postal Museum new building. Basic examination under magnification reassured us that although mould presence could not be excluded, we couldn't detect any dry powdery spores that could be picked up with a brush. Although there still was a smell on the papers, this was most likely due to their permanence in deep sea, rather than to active mould. We also knew that the papers were going to be kept in a controlled environment with low lighting and optimal relative humidity and temperature, unlikely to present the optimal condition for spores to go from dormant to active.
Methylcellulose in a 0.25% solution was used as a re-sizing agent and was applied by brushing. This imparted the items with strength and flexibility with the coating providing much needed surface protection against abrasion and soiling.
Repairs took the longest time given the fragmentary state of most of the items. Reconstructing some of the envelops was particularly satisfying given that in some lucky instance we were able to match them with their respective stamps and letter. Repairs were carried out using Japanese hand-made papers of various thickness, applied with Jin Shofu wheat starch paste.
Preliminary work done in Scotland involved the removal of salt deposits through desalination by soaking the objects in fresh water and the removal of a black slime deposit that had formed on the bundles from the deep sea. However, there was a bundle that arrived to us separately that had not gone through the same process, so desalinisation was performed at the museum using the same methods. This bundle had a very pungent smell that did not wash away with subsequent baths in water. A final bath of 50/50 water and IMS was successful in removing the smell.

Voices from the Deep
Working on this collection was an intense experience and I don't think a more appropriate title for the exhibition that will tell these stories could have been found. These objects do represent voices coming from a not so distant past, from a period that is one of the most tragic in modern history. It was not unusual for ships to carry letters, mail has been carried this way for centuries and it was certainly not unusual for a ship to be sunk and not making it to destination. What is most amazing is that these objects survived to tell the stories of people from all works of life, in their own words. To make the story more poignant is that Christmas was only weeks away when the cargo, with 86 crew members sunk. These letters cover the full spectrum of human emotions - from love to fear to joy and longing - and provide an insight into life and death at the time of WWII.

The letters from the SS Gairsoppa and many other items recovered from the shipwreck can be seen as part of the exhibition Voices from the Deep opening in March 2018 at the Postal Museum, London