This is after John has been through basic. Also, Sherlock hasn't had his last growth spurt yet so he's not as tall as he is in the show.
...
John waited anxiously, scanning the airport. He had sent Sherlock an email the day before yesterday. Sherlock had gotten Mycroft to agree to allowing John and Sherlock to stay in contact but John had no idea how he'd done it. So over the course of Basic Training and RAMC training, John and Sherlock had several conversations and come to an agreement. Sherlock would get clean and John would stay alive.
As long as they kept up their aide of the agreement, everything would be fine. John would visit every leave and Sherlock would make sure to assign a day and a time period for Skype. John had suggested he work with the police. When Sherlock had protested vehemently that he woud never work for the police, John had interrupted him and said, "I know. I'm not saying work for, I'm saying work with. Consult them when they need help."
Sherlock had agreed that he would be okay with that as long as he worked on his own terms.
John's hand tightened around the package. He hoped Sherlock liked it. It seemed suitably dramatic for him.
…
Sherlock tapped impatiently on the divider and said, "Can't you go faste?"
The taxi driver grunted, then said, "What's your rush, kid?"
"Not a kid," Sherlock responded automatically, "And my soldier is getting shipped out today."
"We'll why didn't you just say so? Why my Bill…." Sherlock ignored him and clutched the small package tighter. He hoped John liked it.
….
John sighed as he looked at the plane. Sherlock wasn't coming. Jack, a friend from Basic, placed a hand on his shoulder and said, "Sorry, mate, it doesn't look like your guy's coming."
"I-"
"JOHN!"
John turned in time for Sherlock to barrel into him. Sherlock clung to him and said, "Sorry I'm late the stupid taxi was possibly the slowest driver I have ever seen and then there was and accident we had to go around so I thought I wasn't gunna get here in time and then you'd leave and I wouldn't get to-"
"Breathe, Sherlock." John squeezed Sherlock's shoulders. "I got you something."
Sherlock ducked his head against John's shoulder and said, "I got you something, too."
"Are you gunna let go so I can give it to you?"
Sherlock held on to John tighter. John took him gently by the shoulders and pulled him back a little.
Sherlock relyctantly let go and held his package out to John. He accepted the package John held out to him and then said, "Same time?"
"Yes. On three."
Sherlock grinned and said, "Three."
They both tore off the wrappers. Sherlock held out the coat to study. It was a dark not-quit-navy blue, it would go down to about his ankles. It had many hidden pockets and also seemed to have a water-proof lining. Along one side of the collar, engraved in tiny lettering, was 'Mystery will follow you, Murderers will be found because of you, I will forever belong to you -JW.' He loved it.
John shared at the dog-tag in his hand. 'Could be dangerous -SH'
….
It was an ongoing joke between them. They had been sitting in the hospital and Sherlock had asked why John hadn't really said anything about his drug habit. John had paused before saying, "The drug's are your way of living dangerously. Mine is going into the army. Most people who want their adrenaline going choose to go sky diving or rock climbing. Neither of us are normal."
Sherlock had grinned and said, "So you're saying you're attracted to danger?"
"Yes."
"So if I said, 'could be dangerous' you'd come running?"
"Maybe."
"I'll keep that in mind."
…
John attached the dog-tag to the chain with his others, then hugged Sherlock. I'll call you as soon as possible.
Sherlock hugged him tightly and said, "See that you do."
He watched John until he could see him no longer, then watched his plain take off.