The woman waiting in the nearby car sat for a few minutes before stepping out. The tunnel, as they call it, stretched out before her, flanked at either end by a solitary figure wearing a gown and surgical mask.
As she nervously approached the arch of the green tarpaulin tent, the masked figure offered quiet words of instruction, gently ushering her forward.
There would be someone inside to assist her further she was told, there was nothing to fear.
With that, she disappeared into the darkness. Minutes later, another patient appeared. Then another, and another. Soon they were all lined up, two metres apart, on the banks of the river Liffey, anxiously waiting to step inside the tunnel.
"There is a very stark human face to what we are doing here," Lieutenant Commander Phil Dicker said.
"People are queuing up to be tested for this virus, kids, elderly, all ages, all colours, all creeds, and they are going in to the absolute unknown.
"They have a mask on their face, they are met by people in gowns and masks.
"They're going into a long, dark tunnel where they are not quite sure what is going to happen. They have a sickness of some sort; anyone who is here is sick, they are here for a reason, they have reached the criteria to be tested."
Operation Fortitude, the military response to the Covid-19 crisis, became a visible part of the Dublin city-centre skyline a little over a week ago.
In scenes reminiscent of wartime, the LE Bernard Shaw, a patrol vessel from the Irish naval fleet, is docked close to the Central Bank.
From inside these tents, similar to those used as army field hospitals, staff from the national ambulance service are testing citizens for Covid-19.
The majority flocking to the site are healthcare workers and since testing started on Sunday, their numbers are growing.
"We are due to see 300 today," said Lt Cmdr Dicker.
"On Sunday we started with 126, then we had about 150 on Monday and 150 on Tuesday."
On Wednesday morning, as the crew of the LE Bernard Shaw prepared for another day of testing, Lieutenant Cian Duggan, second in command, stood in the ship's control room, surveying the scene below.
"It does tug on your heart strings when you are dealing with people out on the quay wall," he said.
"But this is something we are prepared for. We have seen it in the Mediterranean and many other operations throughout the history of the naval service."
As well as Dublin, two other Irish navy vessels are berthed in Cork and Galway to assist the HSE with testing .
In the weeks, maybe months ahead, the vessels will act as support bases for onshore testing centres - with testing staff supported by electricity supplies, food preparation, water and equipment storage on the berthed vessels.
There is, however, another important element to their work, the human one.
"Keeping the morale of the HSE staff is a big part of this," explained Lt Duggan.
"We are looking after the welfare of HSE staff by providing things like tea and coffee and masks."
As the most recent addition to the Irish naval fleet, this is the first big operational task the LE Bernard Shaw has been involved in.
Testing is not being done on the ship, but the process starts on board when the lists of patients due to be tested come in via email.
From two lists, one generated by the HSE and one from GP referrals, a single one is generated, printed off and brought to the tents.
The entire ship is a "clean zone" and anyone stepping on or off the shop must adhere to stringent cleaning criteria
Lead medic Jonathan Miloudi oversees screening for every person who steps on board.
"We are taking every precaution," he said."That means enforcing all the guidelines, knowing all the symptoms of this virus and ensuring everyone is screened thoroughly."
Lt Duggan, like many others on the 47-person crew, he is drawing significantly on experience gained during missions in the Mediterranean. Operation Sophia, the European Union's military mission to rescue migrants in the southern Mediterranean Sea, saw Irish naval personnel rescue 18,000 people.
"A lot of that experience transfers directly here," he said.
"For example, we are organising people that are frightened, possibly very ill, otherwise they wouldn't be turning up. So it's about putting them at ease."
The symbolic significance of the vessel has not been lost on Dublin locals, who this week spoke of their relief at seeing the naval presence in the city.
Not for the first time, Covid-19 is being described as the "invisible enemy". For the unit stationed in Sir Rogerson's Quay, specific training on how to respond to chemical, biological and radiological/nuclear (CBRN) incidents, is now being put to use at home.
"Essentially we are dealing with a bio-hazard," said Lt Cmdr Dicker.
"From a personal point of view and from the ship's point of view we know how to manage a biological hazard, which is what we are dealing with here. The virus is the enemy. It's an invisible enemy, but the enemy has friends, it has allies."
On Wednesday, as patients passed through the tunnel outside, Lt Cmdr Dicker was joined below in the officer's mess by members of the crew currently assigned to the Covid mission.
Petty Officer chef Aileen Hanna is providing food on a daily basis to the crew and reservists, working her way through a four-week supply of rations.
"We all have family and friends at home that might have underling illnesses and they are worried," she said.
Nestled together in the belly of their ship, the gathered crew spoke of their desire to see this fight through until the end.
They are everything the defence forces should be, combative, patriotic and steadfast, but they are also human.
As the officers fall silent amid a break in conversation, Lt Cmdr Dicker responds to a question everyone in the country is quietly asking themselves.
"Are you afraid of this virus?"
After a momentary pause he answered, visibly emotional as he delivered a sobering reply.
"Who in the country isn't afraid of his virus? "he said.
But the key message was, he said: "Our previous generation were asked to go to war - our generation have been asked to stay at home. Simple as that."