diff --git a/Cargo.lock b/Cargo.lock
index e70da3a..b49702e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -5,3 +5,61 @@ version = 3
 [[package]]
 name = "advent2021"
 version = "0.1.0"
+dependencies = [
+ "thiserror",
+]
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.32"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba508cc11742c0dc5c1659771673afbab7a0efab23aa17e854cbab0837ed0b43"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "38bc8cc6a5f2e3655e0899c1b848643b2562f853f114bfec7be120678e3ace05"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.82"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8daf5dd0bb60cbd4137b1b587d2fc0ae729bc07cf01cd70b36a1ed5ade3b9d59"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "thiserror"
+version = "1.0.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "854babe52e4df1653706b98fcfc05843010039b406875930a70e4d9644e5c417"
+dependencies = [
+ "thiserror-impl",
+]
+
+[[package]]
+name = "thiserror-impl"
+version = "1.0.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa32fd3f627f367fe16f893e2597ae3c05020f8bba2666a4e6ea73d377e5714b"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8ccb82d61f80a663efe1f787a51b16b5a51e3314d6ac365b08639f52387b33f3"
diff --git a/Cargo.toml b/Cargo.toml
index f399d5b..b7a9c67 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -3,6 +3,5 @@ name = "advent2021"
 version = "0.1.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
 [dependencies]
+thiserror = "1.0"
diff --git a/data/day2_test.txt b/data/day2_test.txt
new file mode 100644
index 0000000..b7172ac
--- /dev/null
+++ b/data/day2_test.txt
@@ -0,0 +1,6 @@
+forward 5
+down 5
+forward 8
+up 3
+down 8
+forward 2
diff --git a/data/day2a.txt b/data/day2a.txt
new file mode 100644
index 0000000..fb1384e
--- /dev/null
+++ b/data/day2a.txt
@@ -0,0 +1,1000 @@
+forward 8
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diff --git a/src/bin/day2.rs b/src/bin/day2.rs
new file mode 100644
index 0000000..4c337f6
--- /dev/null
+++ b/src/bin/day2.rs
@@ -0,0 +1,169 @@
+use std::num;
+use std::str::FromStr;
+use thiserror::Error;
+
+#[cfg(test)]
+const TEST_DATA: &str = include_str!("../../data/day2_test.txt");
+const DAY2A: &str = include_str!("../../data/day2a.txt");
+
+#[derive(Debug, Error, PartialEq)]
+enum Oopsie {
+    #[error("Couldn't understand '{0}' as a command.")]
+    CouldntParseCommand(String),
+    #[error("Couldn't parse number: {0}")]
+    CouldntParseNumber(#[from] num::ParseIntError),
+}
+
+#[derive(Debug, Eq, PartialEq)]
+enum Command {
+    Forward(isize),
+    Down(isize),
+    Up(isize),
+}
+
+impl FromStr for Command {
+    type Err = Oopsie;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        if let Some(rest) = s.strip_prefix("forward ") {
+            Ok(Command::Forward(isize::from_str(rest)?))
+        } else if let Some(rest) = s.strip_prefix("down ") {
+            Ok(Command::Down(isize::from_str(rest)?))
+        } else if let Some(rest) = s.strip_prefix("up ") {
+            Ok(Command::Up(isize::from_str(rest)?))
+        } else {
+            Err(Oopsie::CouldntParseCommand(s.to_string()))
+        }
+    }
+}
+
+fn from_file_data<T: FromStr>(filedata: &str) -> Result<Vec<T>, T::Err> {
+    let mut retval = Vec::new();
+
+    for line in filedata.lines() {
+        retval.push(T::from_str(line)?);
+    }
+
+    Ok(retval)
+}
+
+#[test]
+fn command_parsing() {
+    assert_eq!(Ok(Command::Forward(5)), Command::from_str("forward 5"));
+    assert_eq!(Ok(Command::Down(5)), Command::from_str("down 5"));
+    assert_eq!(Ok(Command::Forward(8)), Command::from_str("forward 8"));
+    assert_eq!(Ok(Command::Up(3)), Command::from_str("up 3"));
+    assert_eq!(Ok(Command::Down(8)), Command::from_str("down 8"));
+    assert_eq!(Ok(Command::Forward(2)), Command::from_str("forward 2"));
+}
+
+#[test]
+fn file_parsing() {
+    let result: Result<Vec<Command>, Oopsie> = from_file_data(TEST_DATA);
+    assert!(result.is_ok());
+}
+
+#[derive(Debug)]
+struct Submarine {
+    interpretation: Interpretation,
+    depth: isize,
+    position_x: isize,
+    aim: isize,
+}
+
+#[derive(Debug)]
+enum Interpretation {
+    Basic,
+    WithAim,
+}
+
+impl Submarine {
+    fn new(interpretation: Interpretation) -> Submarine {
+        Submarine {
+            interpretation,
+            depth: 0,
+            position_x: 0,
+            aim: 0,
+        }
+    }
+
+    fn command(&mut self, cmd: &Command) {
+        match self.interpretation {
+            Interpretation::Basic => match cmd {
+                Command::Forward(v) => self.position_x += v,
+                Command::Up(v) => self.depth -= v,
+                Command::Down(v) => self.depth += v,
+            },
+
+            Interpretation::WithAim => match cmd {
+                Command::Forward(v) => {
+                    self.position_x += v;
+                    self.depth += self.aim * v;
+                }
+                Command::Up(v) => self.aim -= v,
+                Command::Down(v) => self.aim += v,
+            },
+        }
+    }
+
+    fn run(&mut self, cmds: &[Command]) {
+        for cmd in cmds.iter() {
+            self.command(cmd);
+        }
+    }
+
+    fn distance(&self) -> isize {
+        self.depth * self.position_x
+    }
+}
+
+#[test]
+fn basic_test_intepretation() {
+    let test_commands = from_file_data(TEST_DATA).unwrap();
+    let mut test_submarine = Submarine::new(Interpretation::Basic);
+    test_submarine.run(&test_commands);
+    assert_eq!(150, test_submarine.distance());
+}
+
+#[test]
+fn test_intepretation_with_aim() {
+    let test_commands = from_file_data(TEST_DATA).unwrap();
+    let mut test_submarine = Submarine::new(Interpretation::WithAim);
+    test_submarine.run(&test_commands);
+    assert_eq!(900, test_submarine.distance());
+}
+
+// just in case I decide to be fancy and pull some stuff out of this for a
+// later challenge
+#[test]
+fn regression_tests() {
+    let commands = from_file_data(DAY2A).unwrap();
+
+    let mut part1_submarine = Submarine::new(Interpretation::Basic);
+    part1_submarine.run(&commands);
+    assert_eq!(2039912, part1_submarine.distance());
+
+    let mut part2_submarine = Submarine::new(Interpretation::WithAim);
+    part2_submarine.run(&commands);
+    assert_eq!(1942068080, part2_submarine.distance());
+}
+
+fn day2() -> Result<(), Oopsie> {
+    let commands = from_file_data(DAY2A)?;
+
+    let mut part1_submarine = Submarine::new(Interpretation::Basic);
+    part1_submarine.run(&commands);
+    println!("Part 1 distance: {}", part1_submarine.distance());
+
+    let mut part2_submarine = Submarine::new(Interpretation::WithAim);
+    part2_submarine.run(&commands);
+    println!("Part 2 distance: {}", part2_submarine.distance());
+
+    Ok(())
+}
+
+fn main() {
+    if let Err(e) = day2() {
+        println!("Whoops: Top-level error: {}", e);
+    }
+}